Infinity is that which is boundless, endless, or larger than any natural number. It is often denoted by the infinity symbol. In the 17th century, with the introduction of the infinity symbol and infinitesimal calculus, mathematicians began to work with infinite series and what some mathematicians (including l'Hôpital and Bernoulli) regarded as infinitely small quantities, but infinity continued to be associated with endless processes.

Source: Wikipedia