Hacking is looking at the rules and finding smart ways of following them. A lawyer or accountant finding legal loopholes is hacking.
The clearest place to see hacking is within games where one follows the rules and does not cheat.
Avoid thinking that hacking is unethical behaviour. A common mistake of people that don't understand the culture.
Like many great words, the meaning does depend on who uses the word. But the people who created the usage didn't use it for cheating.
My answer that got me accepted was that there was a lip syncing competition at my college that was dwindling because everyone had to submit a CD and sign up in advance. It also was held in an auditorium.
When I took over, I moved it to Spotify and moved the venue to the lawn, and we went from ~20 people the previous year to 1.2k the year I ran it.
Here's pg's definition of a hacker: https://www.paulgraham.com/gba.html
I left out that the rule at the time was all songs had to be reviewed by the administration, which I didn't comply with. I'm not saying my story is the greatest; quite the opposite. I was trying to show that "hacking" isn't inherently unethical or even particularly interesting.
Why should they put their own life on the line when there are so many others whose lives could be used instead?