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 difference between an allegory and a symbol is that an allegory is a complete narrative that conveys abstract ideas to get a point across, while a symbol is a representation of an idea or concept that can have a different meaning throughout a literary work.