three-point landing (aircraft operation). A full-stall landing of an airplane equipped with a tail wheel. In a three-point landing, the main wheels and the tail wheel touch the ground at the same time. A three-point landing with a tail wheel airplane is desirable, but landing an airplane with a nose wheel so the main wheels and the nose wheel touch the ground at the same time is not normally considered a good operating procedure.
three-pole, single-throw switch. An electrical switch that has three sets of contacts, controlled by a single operating handle. A three-pole, single-throw switch can select two conditions, such as on and off, in three separate circuits.

three-state buffer. A digital logic device used as a switch in an integrated circuit chip. When there is a logic low on the control line, the device acts as a closed switch with the in and out lines connected, a low on the in line produces a low on the out line, and a high on the in line produces a high on the out line. When there is a high on the control line, the device acts as an open switch, placing a high impedance between the in and the out lines.

three-view drawing. An orthographic drawing showing three views of a part. There are six possible views, but the three most commonly used for aircraft drawings are the front, right-side, and top views.
three-way light switch. A type of switch that allows an electrical light to be turned on or off at either of two locations. Three-way light switches are used at the top and the bottom of stairs and at either end of a long hall.