What does it mean to raise a number to a negative power?

A negative exponent is exactly the same as a positive one with one major exception: a negative power means divide 1 by that number. Sounds complicated but if you see it it's much simpler.

2=2/1

25=25/1

2^2=(2^2)/1

25^2=(25^2)/1

2^-2=1/(2^2)

25^-2=1/(25^2)