Power feeding is intentionally over-feeding your snake by any of several different measures. A lot of individuals will feed their snake a prey item that is larger than recommended in comparison to the size of their snake, or they'll feed the animal a prey item, and then, as it's swallowing it, they'll jam another pre-killed prey item into the snake's mouth so he has no choice but to ingest that one as well. Or, they'll feed the animal a few times a week, as gncz73 mentioned.

This is terrible for the following reasons:

a. the snake's immune system suffers because it is a tremendous shock to the snake's internals to have to constantly digest larger than acceptable prey items, and it is also a shock to their system to have to begin digesting a new prey item right after digesting the previous one. All the efforts of the snake's system get dedicated to digestion, and this weakens the snake's system over-all, thus, weakening the immune system as well

b. the animal can, in certain cases develop "fatty liver" which is a health problem shown to develop in snakes that are continually fed large rabbits and adult guinea pigs

c. it dehydrates the snake, because the snake needs fluids to help digest its prey, if it eats too much, or the meals it eats are too large it robs the snake of necessary fluids that help sustain the over-all health of the animal

Power feeding is bad news ... Repeatedly shocking a snakes system like that reduces their life-span by numerous years. Always stick to a conservative feeding schedule.

My snakes eat on a conservative feeding schedule and believe me, they're much happier and healthier