A term used to refer to the measurable ki levels of characters in Dragon Ball. It was a system introduced in the Saiyan saga and dropped after the Frieza saga, since it made no sense and was completely inconsistent. Many people still try to use the power levels to try to measure actual abilities, often making up fake power levels for characters later in the series. Many people also try to give power levels to characters from other series, of course this exercise is rather pointless.
Likely inspired by DBZ, many other series use a "power level" like system.
- Bastard!! used a power - level type system in the later parts of the manga, but again, it doesn't seem to logically correlate to observed abilities beyond the simple idea of "character with higher PL is stronger"
- Ghost Sweeper Mikami introduced a system late in the manga known as "might" which seems to function like a power level scale
- Katekyou Hitman Reborn! has "Flame Volts" (often referred to as just FV), which, instead of measuring the overall power of different characters, measure the strength/power of individual attacks and releases of energy
- One Piece used a system called "Douriki" during the Water 7 and Enies Lobby arcs. OPtards have attempted to use this system to calculate speeds and such, despite the fact that it has even more limitations than DBZ power levels (for example, it doesn't take into account Devil Fruit abilities, and it was stated that an armed marine had a douriki number of 10. So anyone trying to use this to calculate speed must believe that a marine holding a gun magically makes him faster)
- Negima somewhat parodies this concept, with Jacobus Rakan's list, which includes such things as tanks, modern Aegis battlecruisers, etc. It's really up to the reader how seriously you want to take it
- Nipponverse levels work this way as well, although in addition to the normal problem, some of them are determined by game mechanics, and thus invalid
- Shaman King measured Furyoku and Reiyoku in this way - it really isn't any more reliable than the others
- Toriko has animals ranked by "Capture Levels", indicating how difficult it is for a hunter to capture them
- The attack/defense points of various monsters in Yu-Gi-Oh could be considered a form of power level system
- Yu Yu Hakusho introduced power levels during the 3 Kings Saga. Again, they are pretty meaningless for determining anything other than which YYH character is stronger than which other YYH character
The term can also be used to refer to the general power of a fictional series, for example, you could say "One Piece has a higher power level than Naruto".