Concentration
Concentration is the share of a bankroll exposed to a single outcome or a single event at one time.
In plain English
Several bets can look independent while resolving on the same underlying result. Adding them up is the only way to see true exposure.
Example
Backing a team on the moneyline, the spread and a player total is largely one bet on that team playing well.
Why it matters
Unnoticed concentration is how a bankroll takes a much larger hit than the staking plan intended.