Nil
A quantity is said to be nil, or negligible, if it is small enough that it can be ignored. Nil is closely related to the standard mathematics concept of an infinitesimal, but it is not the same. Nil is also closely related to the concept of zero.
References
The name nil for this concept was, I think, coined by Harry Binswanger in his lecture Saving Math from Plato. [TODO rephrase or put this elsewhere in the document]