Gradual loosening of an integrated circuit ("chip") in its socket as a result of expansion and contraction during the normal heating and cooling cycles of an electronic system, combined with vibration, e.g. due to cooling fans. The chip can loosen to the point that poor electrical contact between chip and socket reduces the signal quality, causing failure. Pushing chips back into their sockets can cure such symptoms temporarily. Permanent solutions include soldering chips directly to the PCB and clipping the component into the socket (as on some in-line memory modules).
The same phenomenon can affect anything plugged into a socket but not held securely in place, e.g. a circuit board plugged into an edge connector on a motherboard or backplane can suffer "card creep".