Daily loss limit
A prop firm rule: the maximum amount you can lose in a day (usually 4-5% of the starting balance); open-position losses count too.
The calculation varies from firm to firm: based on the start-of-day balance or on equity, fixed or trailing; read the rule text. Breaching the limit means the account is closed at most firms.
Practical rule: set your risk per trade so that you use at most half of the daily limit; two or three consecutive losses shouldn't push you close to the limit.