Logic: tokens vs types

Understanding the token-type distinction is fundamental in logic. A type is an abstract concept of a token. A token is an instance, a concrete existance of a type. A token can take a lots of forms, written, auditory or even graphical. For example if tow people want to create a token representing the type 'Bird' they would write the word bird, bIrd, Bird .... Thus the word 'Bird' even if it is written exactly the same by tow persons, those tow words are tow tokens of the same type (the concept of a bird)!

A good read on the subject is : The laws of truth - Nicholas J Smith