A connection to an electrical device made by simply pushing the wire into a hole instead of screwing it down.
A "backstab" is using the push in connectors often provided on the backs of switches and receptacles. It makes for a quick installation but, while code-compliant, is often frowned upon as it can work loose over time (especially on receptacles where the device flexes every time a plug is inserted or removed), potentially causing arcs and fires.
It is preferred to use the screw down connections on these devices to provide a more solid mechanical and electrical connection.
