The Torx fastener is a type of threaded fastener, or bolt, invented1 by General Motors in the 1960s. The head of a Torx fastener has a splined hole in it that looks something like a six-pointed star. Naturally, there are splined drivers to fit these holes. They're designated by a series of numbers such as T-8 or T-10.
The Torx fastener was developed for two reasons. First, the splines in the hole increase the contact surface between the tool and the fastener and thus make it possible to transmit increased torque when tightening the fastener with less danger of stripping the head or rounding the tool (hence the name). Second, like most new fastener heads, the tooling was originally very difficult to come by, and so things put together with Torx fasteners were harder for the average consumer to disassemble. This is the mechanical equivalent of the 'security through obscurity' principle sometimes practised in the computer industry.
Nowadays, of course, Torx bits are easy to buy in almost any auto parts store. This is a good thing, because the alternative was to use an Allen wrench, which tends to make quite a mess of the fastener head. Many small electronics tool kits include Torx drivers now, particularly those aimed at Macintosh users, since Apple also wholeheartedly adopted this fastener type.