From The Apple Wiki

Userland describes the software running on an iOS device after the kernel has started. A userland-based exploit or jailbreak, being entirely software-based, can be patched by Apple. Userland jailbreaks differ from jailbreaks that affect the boot chain of trust, in that they do not allow custom firmwares/IMG3 files to be flashed.

Existing userland jailbreaks include JailbreakMe Star and Saffron. Other userland jailbreaks include Spirit, Absinthe, evasi0n, and Pangu.

For more context: Wikipedia on what "userland" means.