/System/Library/Frameworks/QuickLookUI.framework/Versions/A/XPCServices/QuickLookUIService.xpc/Contents/MacOS/QuickLookUIService QuickLookUIService is a background process on Mac that's responsible for file previews displayed by Quick Look, Spotlight, etc. It can also be employed for 'Open and Save Panel Service' by apps like Preview or third-party software like Google Chrome.
The binary is a part of QuickLookUI public framework.