The transporter platform (or transporter pad) is a component of the transporter system, where the individual or object that is being transported must be placed in order to be successfully transported. Some transporter systems support site-to-site transport and do not require the use of the transporter pad at all.
Cargo platforms have one large transporter pad, (TNG: "Power Play") while personnel platforms consist of six smaller transporter pads; the number of pads may vary according to the type of ship.
Each pad has four redundant molecular imaging scanners so if one of the scanners fails the other three takes over. When necessary, the entire platform can be enclosed within a force field. (TNG: "Realm of Fear")
Cardassian space stations were designed with transporter pads in ops.
Background
In "The Cage", the actual transporter pads were clearly split by three colors, mirrored from front to back: yellow, blue and green, presumably correlating to the Starfleet uniform division colors of the period. Starting with "Where No Man Has Gone Before", the individual pads were all uplight by white light only for the remainder of TOS.