The most commonly referred-to meter. When someone says things about ‘meter’, it’s usually this one, because it’s usually the only one you have direct control over.
A character that is good at charging meter (e.g., to pass on more to other teammates) may be known as a “battery”.
On its face, it is supposed to be expended on big moves like super special moves, but in some games, it can be expended on other things like juiced up special moves, super cancels, and guard cancels; depending on the game’s balance, these secondary functions may actually be more useful more often.
The specifics depend on the game, but the most common factors are making attacks, taking attacks, and blocking attacks. In some games, you may have a gauge-charger that allows you to advance the process manually.
It may be divided into levels or percentages; basic units are called “stocks”. These stocks are usually held over for subsequent rounds, and in some games, partially-charged stocks are also held over.
The upper limit for stocks is usually three or five levels. The extreme upper limit has been 99 (in the Darkstalkers series).
There are a lot of differences, with a lot of different names, but when it comes down to it, they are pretty much power meters.