1. Mediocrity, Par, Nothing Special. 2. A backhanded way of telling someone what they did was mediocre. 3. A funny terminology used to passively/aggressively make fun of mediocrity.
"These tacos aren't the worst I've ever had. These tacos are hella decent."
"YoBrad Bro! That cover of Crazy Town's Butterfly you did last night was hella decent bro!"