Actuation refers to the point when a keyswitch changes from being open to being closed, i.e. the point when the keyboard will register a keystroke. The actuation point can also be referred to as the "make" point. In quality switches, the actuation point occurs before full travel, i.e. before the switch is bottomed out; typically actuation will occur at half travel, but this varies betweens switches. Typical discrete switches have 3.5–4 mm of travel, with actuation around 2 mm. Membrane rubber dome switches only actuate when fully depressed.
Release refers to when the switch returns to its default closed state, i.e. the keyboard detects that the key has been released. This can also be referred to as the "break" point.