A Bluetooth profile (mode) that enables a Bluetooth device to transfer (push) an object (file) to another Bluetooth device.
Examples include sending contact info or a calendar event from a phone to a another phone, sending a photo from a phone to a desktop computer, or sending a document file from a phone to a tablet.
Not all Bluetooth devices support OPP. Some Bluetooth phones that do support OPP only support sending contact info and/or calendar events (in the vCard format).
OPP is a sub-profile of the OBEX profile, and OPP functionality is often referred to as "OBEX".