In mathematics, infinity is the conceptual expression of such a numberless number. It is often symbolized by the lemniscate (also known as the lemniscate of Bernoulli), which looks something like the numeral 8 written sideways (). This symbol for infinity was first used in the 1600s by the mathematician John Wallis.
An epic is a poem; most epics started as oral tales that were passed down from generation to generation (often in the form of songs), which is why they're poems. A legend and a myth are more similar, but a myth most often explains something about the universe. So while there might be a legend about a man who slayed all the dragons, a myth would be about the man who caused it to rain, or how humans were created. Those are the basics differences.
The major difference between Epic and other Games Workshop games is that instead of a player moving and firing all of his forces at once, players take turns moving one or two formations at a time using a variety of different orders, giving the feeling of a battlefield developing in real-time, and also resulting in a game that is more tactically complex than Warhammer 40,000.