Searing food means browning meat quickly on very high or moderately high heat to seal in the juices. This ensures that the meat is tender and soft. Normally, the inside of the meat is still rare or half-cooked. As such, it needs to be cooked over a low heat for a longer period of time.
A dry-heat cooking technique in which the surface of a food is browned quickly over very high heat; often done to add colour and flavour as the first step in a combination cooking method.
Kind of a catch all term for using high temp direct heat to brown the outside of meat, usually in a pan with some oil, butter or fat, although they aren't necessary. You might also call this pan-broiling.