A sport with a dog and person competing as a team, for time, on an obstacle-type course. There are jumps, tunnels, teetertotters, weave poles, dogwalk, Aframe, broadjump, other spread jumps and other possible obstacles that the dog must go over, through, across, weave between in a preordained and specific manner and order. Fastest time with the fewest faults for mistakes, wins. Based on horseshow jumping. Only dog takes the obstacles. Person must handle, run with dog, off leash without toys or treats, or touching dog or obstacles. Runs that count (qualify for some title) are called Q's. Also there are Double Q's and Super Q's, and dirty Q's. Agility tends to produce its own language.
Agility is used in Diablo and other games, it is usually ascociated with stats and abilities. Agility it'self actually means to be agile and agile means to be quick or fast, probably for running fast and dodging attacks thrown at you.
1 Agility increased by 2, you can run faster.
2 Wow, that thing was Agile!