Infinity: A (deprecated) tool making LCFW permanent on newer models.
XMB (XrossMediaBar): The main menu interface.
VSH (Visual Shell): The technical name for the XMB and its underlying system.
VSH Menu: A quick settings menu accessed on the XMB.
Recovery Menu: A low-level boot menu for fixing issues or tweaking system settings.
POPS (PlayStation One Portable Station): The official PS1 emulator.
PBP: The executable package format for PSP games and updates. Usually, EBOOT.PBP is the main executable.
PRX / SPRX: Relocatable executable modules (plugins and system files).
ISO / CSO: Backed-up UMD games. CSO is a compressed format.
PSAR: An archive format often used in official firmware updates.
PMF: PSP Movie Format (video).
PGF: PSP Font Format.
RCO / QRC / RAF: Resource container files used for XMB themes, sounds, and icons.
Overclock: Running the PSP faster than the default speed. This usually meant bumping it to 333MHz, but developers recently figured out how to push it even further up to 500MHz.
OTA Update: Over The Air updates. You can download and install new ARK firmware updates directly from the PSP over Wi-Fi.