With the introduction of protected mode it became possible for programs to run in isolated memory spaces where they are unable to impact other programs running on the same CPU. These programs were said to be running “in a jail” that limited their access to the rest of the computer. A software exploit that allowed a program running inside the “jail” to gain root access / run code outside of protected mode was a “jailbreak”.

I still miss the narrow window in which you could make use of paging without technically being in protected mode. Basically there was like one revision of the 386 where you could set the paging bit but not protected mode and remain in real mode but with access to paging meaning you got access to paging without the additional processor overhead of protected mode. Not terribly useful since it was removed in short order, but neat to know about. Kinda like how there were a few instructions that had multiple opcodes and there was one commercially distributed assembler that used the alternative opcodes as a way to identify code assembled by it. Or POP CS - easily the most useless 80086 instruction, so useless that the opcode for it got repurposed in the next x86 processor.