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a quick release system, also known as QRS is, in the photography world, a device that allows you to quickly join and separate a camera and a tripod (usually a tripod head).

The need for such a system is obvious, if you have ever tried to use on of the cheap or obsolete tripods that can't have one: screwing the camera to the tripod takes forever, and the connection is never too good --- it is very easy to turn the camera in the direction that unscrews the screw. On the other hand, repeatedly tightening the screw hard will eventually wear it.
Enter the QRS: it consists of two pieces, a female and a male.
The female one is fixed to (or integral with) the tripod head and features some sort of spring-powered clever gizmo that grabs the male part: this, in turn, is screwed to the camera body. The male part is usually called the plate, and it can be rectangular or hexagonal.

Ignoring the obvious sexual overtones, quick release systems differ in quality (cast aluminum vs. machined steel), safety and price.

Will it improve my photography ?

It usually will: a QRS makes using a tripod faster and more comfortable, which means that you will use your tripod more, which means that you will be able to catch nicer light, get sharper pictures ... generally speaking, it will extend your photographic possibilities.
Did I already mention that tripods are very good ?