Defining a power limiter depends upon application.
Power limiters are mostly used at microwaves, to protect sensitive devices from an excessive power. Such limiter often use a pair of detector diodes connected back to back; opening each P/N junction "swallows" a part of input power and only a small fraction (leakage) passes to output. Other limiters use PIN diodes controlled by detector diodes, and the like.
Power limiters are used in electrical and mechanical systems to prevent damage. Usually there is a power sensor and a threshold detector which, upon exceeding a limit, cuts or blocks the input power. Such devices utilize feedback and can be quite complex.
You can build a simple power limiter to block high noise levels from a loudspeaker. Connect two silicon diodes back-to-back across speaker terminals- it allows you to hear a moderate volume while a higher volume is "swallowed" by the diodes.