Reference · Updated 2026-05-04

Glossary — CS2 skin market and STI methodology

20 definitions covering CS2 skin terminology and index methodology terms used across the Skin Trackers editorial. Each definition links to longer-form coverage in the relevant blog post or methodology page.

CS2 Skin Terminology

Pattern Index: An integer between 0 and 1000 randomly generated when a CS2 skin instance is created (case opening, drop, trade-up contract). Permanent and immutable — baked into the item ID. For most skins, pattern is cosmetic noise; for a small subset (Case Hardened, Doppler, Crimson Web, Marble Fade), specific pattern indices produce visually-rare effects that command 5x to 100x premiums over the average pattern.
Float (Wear): A decimal value from 0.00 to 1.00 representing the surface wear of a CS2 skin instance, generated alongside the pattern index at creation. Lower float = less wear = higher visual quality. The float maps to a wear category: Factory New (0.00-0.07), Minimum Wear (0.07-0.15), Field-Tested (0.15-0.38), Well-Worn (0.38-0.45), Battle-Scarred (0.45-1.00). Float is the primary price differentiator on most skins (alongside StatTrak).
StatTrak™: A meta-attribute on roughly 1 in 10 CS2 skin instances that tracks confirmed kills with the weapon. Adds a counter visible on the model. StatTrak skins typically trade at 10–50% premium to the same skin in non-StatTrak form, with the premium varying by skin tier (lower-tier skins often see 30%+ premium, blue-chip skins see closer to 10–20%).
Souvenir: A skin variant that drops only from Souvenir Packages awarded to viewers of professional CS2 majors. Souvenirs always carry team and player stickers from the match they were dropped at, making the rarest combinations (e.g. AWP Dragon Lore Factory New with iBUYPOWER Holo Katowice 2014 stickers) some of the most valuable items in the game. Souvenirs are a separate inventory tier from regular drops.
Steam Market Cap: The technical $1,800 ceiling that the Steam Community Market enforces on any single listing. Items priced above this cap cannot be sold on Steam Market and trade off-market only (CSFloat, Skinport, peer-to-peer). The cap effectively splits the CS2 skin market into two regimes: ≤$1,800 (high liquidity, transparent pricing) and >$1,800 (illiquid, opaque pricing). The STI 500 and STI 1000 indices apply a $1,800 inclusion ceiling to stay within the liquid regime.
Doppler Phase: One of 5+ distinct color outcomes on Doppler skins, determined entirely by the pattern index. Phases: Phase 1, 2, 3, 4 (purple/pink with accent colors, baseline price), Ruby (solid red, 2-3x premium), Sapphire (solid deep blue, 3-5x premium), Black Pearl (pearlescent black, 4-8x premium), Emerald (Gamma Doppler only, solid green, top tier). Phase identification requires inspecting the item — Steam Market does not expose the phase in listings.
Case Hardened Blue Gem: A pattern-rare outcome on AK-47, Five-SeveN, Karambit, and Bayonet Case Hardened skins where the receiver/blade lands with high blue saturation. Pattern #661 is the canonical 'perfect blue gem' (50-100x average), with a tier system below it: Tier 1 (50-65% blue, +150% to +250%), Tier 2 (35-50% blue, +60% to +120%). Pattern grading is community-consensus based, not Valve-issued — references include csgomarketforum and individual collectors like csgo_blue_gems.
Contraband: An exclusive rarity tier created in 2014 when Valve removed the M4A4 Howl from active distribution due to plagiarism issues with the original artwork. M4A4 Howl is the only Contraband skin — meaning it cannot be obtained from any case, collection, or operation, and existing copies are fixed in supply. The Contraband tier is the most extreme example of supply scarcity in CS2.
Drop Pool: The set of weapon cases currently active in CS2's random drop system. Items in cases that have been removed from the drop pool cannot be newly created — they only exist in inventories that already opened them historically. Valve removes cases periodically (the Sealed Genesis Terminal release in 2025 was the most recent major change to the acquisition mechanic in over a decade), creating structural supply scarcity that drives long-term price appreciation.
Trade-up Contract: A CS2 mechanic that consumes 10 skins of the same rarity tier and outputs 1 random skin from the next-higher rarity tier within the same collection. Trade-ups are an alternative skin generation source beyond cases and drops. Their economic effect is to compress the supply of low-tier skins and expand the supply of mid-tier skins within active collections. STI methodology treats trade-up output as ordinary creation events.

Index Methodology

Market-cap Weighted Index: An index construction methodology where each constituent's weight is proportional to its market capitalization (price × supply). The S&P 500 uses market-cap weighting; STI 30/100/500/1000/Cases all do too. The alternative — equal-weighted — gives every constituent the same weight regardless of size. Market-cap weighting is the standard for broad-market benchmarks because it tracks the actual flow of capital through the market.
Divisor Adjustment: A mathematical mechanism used by S&P Dow Jones (since 1957), Dow Jones (since 1928), and the STI family to keep the index value continuous when the constituent basket changes at rebalance. When a skin enters or leaves the basket, the divisor is recalibrated so the index value the moment after rebalance matches the value the moment before — eliminating artificial jumps in the chart caused by methodology changes rather than real market movement.
Rebalance: The scheduled moment when an index recomputes its eligible universe, constituent set, and weights from current data. STI 100, 500, 1000, and Cases rebalance monthly; STI 30 rebalances quarterly (matching S&P 500 cadence). Cadence is a methodology choice with explicit trade-offs: monthly responds faster to structural shifts but introduces more noise; quarterly smooths the chart but lags the universe.
Sharpe Ratio: A measure of risk-adjusted return, computed as (asset return − risk-free rate) ÷ asset volatility. A positive Sharpe means the asset paid more than the risk-free alternative for the volatility taken. The STI family reports Sharpe versus CDI (Brazilian risk-free rate) over the 6-year backtest: STI 30/100/500 are negative (broad skin market underperformed risk-free per unit of volatility), STI Cases is positive (+0.96).
Maximum Drawdown: The largest peak-to-trough decline an asset experienced during a measurement window, expressed as a percentage. Maximum drawdown captures the worst-case loss that an investor holding the asset throughout the window would have endured. STI 500's maximum drawdown over 2020-2026 was approximately −38% (the post-September-2025 Genesis Terminal release crash). Compares to S&P 500 max drawdown ~−25% over the same window.
CAGR (Compound Annual Growth Rate): The constant annual rate of return that, if compounded, produces the actual total return over the period. Computed as (end_value / start_value)^(1/years) − 1. STI Cases CAGR over 6 years: ~41.5%/year. STI 500 CAGR: ~8.7%. CAGR is the standard way to compare returns across assets with different total durations and is what 'annual return' means in financial reporting.
Annualized Volatility: The standard deviation of an asset's returns, scaled to a 1-year measurement window for comparison. Computed as monthly_std × √12 for monthly data. STI 30 annualized volatility: ~30%. STI Cases: ~44%. S&P 500 over the same window: ~16%. Higher volatility means larger swings around the mean and informs the Sharpe ratio denominator.
Survivor Bias: A backtest distortion where assets that failed (delisted, went to zero, stopped trading) are excluded from the historical analysis, inflating the apparent return of the surviving subset. Skin market analogy: a skin that crashed 90% and stopped trading would, in a no-rebalance system, remain in the basket at its stale price. STI mitigates survivor bias by recomputing the universe at each rebalance and dropping ineligible items, with their historical contribution preserved.
Look-ahead Bias: A backtest distortion where the methodology was tuned with knowledge of the data it would be applied to, inflating apparent performance. Mitigation: publish inclusion rules explicitly so a reviewer can verify the methodology was fixed before the data, not adjusted after. STI methodology is documented in /en/methodology and /metodologia for this reason.
Liquidity Penalty: The structural drag on after-friction returns experienced by illiquid assets. For CS2 skins, the liquidity penalty has multiple sources: 15% Steam Market fee, days-to-weeks holding period to clear above-cap items, bid-ask spreads, and the fact that broad-market replication requires actually trading 2-8 items per month for STI 500. Quantified in the cross-asset post: STI 30 trailed S&P 500 by ~100pp over 6 years primarily due to this penalty, not skin-quality differences.