The site-to-site transport interlock was a component of the transporter system, designed to permit site-to-site transport. Deactivating the interlocks required transports to either originate or end on the transporter pad.
In 2367, Miles O'Brien deactivated the interlocks in an attempt to thwart Commander Data, who had seized control of the USS Enterprise-D and taken it to Terlina III. The attempt failed, as Data used a series of force field commands to reach Transporter Room 1 and reactivate the interlocks. (TNG: "Brothers")