Robust Equity
Basic Definition
Robust equity refers to a hand in poker that has a strong equity (winning percentage) against an opponent's range. It describes a hand that demonstrates relatively stable strength against a wide variety of opponent hands.
Specific Situation
If your hand is 
and the flop is 

, drawing an Ace or a 9 will complete the nuts, making this open-ended equity robust.
Your hand is 
, and the flop is 

. This hit on the 5 is easily overturned on the turn or river, so the equity of this hand is not robust (vulnerable).
Important Information
A hand with robust equity is less affected by the strength of the opponent's range, making it easier to play aggressively.
Focusing too much on robust equity might prevent you from effectively considering post-flop developments when your opponent's range is narrow.
Examples of Term Usage
"In hands with high robust equity, large bets are often recommended."