What you call a book that is very interesting, and you just can't put it down. You are trapped inside the book, like you are in an arena. A cool new way to describe a book nowadays.
Did you read Catching Fire yet? I love the arena in that book!" "NO thanks for spoiling it!" "No I mean like the arena. Like you are trapped inside the book, like you would be in an arena..." "OH I get it!
The area of memory attached to a process by brk(2) and sbrk(2) and used by malloc(3) as dynamic storage. So named from a malloc: corrupt arena message emitted when some early versions detected an impossible value in the free block list.