The first purpose-made RC connector most of us used. There are 2 kinds of these T-Plug connectors on the market, authentic W.S. Deans Ultra Plugs (usually referred to as "Deans" by the world) and a handful of clones. Authentic Deans Plugs are widely accepted to be superior compared to the clones but the clones offer other benefits including greatly lower cost and the addition of ribs on some models to make the connectors easier to disconnect. In general "Deans" are considered to be difficult to solder, especially for wire larger than 12awg, and difficult to connect/disconnect.
Note: this is the female connector only!