What is pent up energy?

When you haven't had sex in an incredibly long time or are a virgin that desperately wants to bone and your sexual desire is so fuckin high that you feel like your dick/pussy is gonna explode

Damn man I haven't had sex since 2009, I've got so much pent up sexual energy

pent up energy - video

Pent up energy - what is it?

It means you aren't getting any, and you want some.

Sara had a lot of pent up energy because she wasn't getting any from Max.