In game studies, triangularity refers to what Jesse Schell calls "balanced asymmetric risk" (Schell 181). This is the situation that arises when a player is faced with a choice between two actions: one that is low risk and gives a low reward, and another that is risky but has a bigger payoff. According to Schell, this is a good way to acheive game balance.
Low risk/low reward High risk/High reward
\\ //
\\ //
\\ //
\\ //
\\ //
\\ //
Player