A Microsoft file hosting and synchronization service.
biggest pies of crap software. so unintuitive .... just use google one drive and store ur files there or a usb drive. it installs files i had like 6 years ago. just uninstall it as soon as windows boots up so it doesnt start syncing random files. it started to sync program files folder for me... WHY WOULD YOU MAKE IT DO THAT. it syncs random files from programs not even installed