Infinitesimal may mean infinitely small in most people’s dictionaries, or bring up thoughts of subatomic particles. To those who study arithmetic, however, it may mean numbers greater in absolute value than zero, yet smaller than any positive real number.

But for those who study calculus, it is an area of mathematics pioneered by Gottfried Leibniz. His idea was based purely on the concept of infinitesimals; this was in opposition to the calculus of Isaac Newton, who based his calculus on the concept of the limit. Although historically the emphasis was placed on the minute, modern infinitesimal calculus actually has little to do with infinitely small quantities.