Image sprites are a way to reduce the number of HTTP requests by combining multiple images into one file and displaying parts of it as needed.
.icon {
background-image: url('sprite.png');
width: 50px;
height: 50px;
}
.icon-home {
background-position: 0 0;
}
.icon-search {
background-position: -50px 0;
}
Supported by all major browsers.