Unauthorized use, or attempts to circumvent or bypass the security mechanisms of an information system or network.
Reverse engineering (RE) is the process of taking something (a device, an electrical component, a software program, etc.) apart and analyzing its workings in detail, usually with the intention to construct a new device or program that does the same thing without actually copying anything from the original. The verb form is to reverse-engineer, spelled with a hyphen.
When you have fully reverse engineered a piece of software then you completely understand how it works. That doesn't mean you also 'hacked' that piece of software. Does installing a hacked drive makes you a hacker? No ofcourse not, that's just plain silly. You didn't circumvent any security mechanisms, the original author of the firmware hack did.