Meter has many uses in this game it seems, which is fantastic. I think there's 6 different things you can use meter for in Injustice.
EX moves: Not really traditional EX moves, but they essentially change the property of specific special moves of a character. These cost 1 meter
Push Block: Pretty self explanatory. If someone is pressuring you with block strings, you can push block at the cost of 1 meter. This pushes them back so they're no longer on top of you.
Meter Burn on Stage Interactables: You can meter burn on some interactables to give them armor.
Armored Wall/Ground Bounces: f3 and b3 are the universal ground and wall bounces for every character. You can add armor to them by meter burning them. This costs 1 meter.
ABC (Armored Bounce Cancel) Aka "FADC": You can cancel a normal into FF or BB, Meter Burn, then you can dash away, dash towards, or follow through with the wallbounce or groundbounce. This costs 2 meters.
Clash/Wager: After your first life bar has depleted, you're able to activate wager mode. You activate it while being combo'd, much like a breaker in MK9. You then wager meter, whoever wages the most meter gets a certain bonus. If you wage the same amount, neither player gets a bonus, and you end up in a neutral position with one another. Also, each player only gets one per macth.
Super: Pretty standard. Like X-Rays in MK9, or Supers in other fighters. You burn all your meter for a high damaging, cinematic attack that does good damage. Not usually worth it though, especially in a game where you can utilize the meter so much.
Is there anything else you can use meter for in Injustice?