In philosophy a token is an single instance or occurrence. This is usually used when talking about ontology.
This writeup is a token of a writeup, this R is a token of both 'R' and of a letter. You can also have tokens of qualitative properties, such as red. Tokens are not used to refer to quantitative properties, such as weight.
Tokens are in contrast to types or kinds. A type refers to an abstract object (writeups, letters), while a token refers to a specific instance (this writeup, this R).