Is there a theme for this jam or is it just do whatever you want.

It's do whatever you want, with the option to create a game based on a theme if you so choose. Per the jam's description:

"BONUS THEME IF YOU HAVE NO IDEAS:

A game about being chased by a monster, basically a cave maze where you have to find the exit before the monster catches you."

the theme is completely optional, you can do whatever you want for it.