Effective stack is the smaller stack size between you and your opponent, determining maximum risk.
Explanation. In a heads‑up or all‑in pot, the smaller stack caps how much can be risked or won. The term reflects the idea of “effectively” how many chips can be contested. For instance, if you have 100bb and your opponent has 50bb, the effective stack is 50bb. Accurate assessment of effective stack size is crucial for decisions on bet sizing, playability, and risk management.