Definition

The key word here is "token". The word has multiple meanings. The most prominent and relevan for our paper are the following:

1. A piece representing money, but issued by an entity other than the government:
   1.1. A casino chip
   1.2. A unit of cryptocurrency also known as fungible tokens
   1.3. A voucher or a gift card (providing a limited amount of money in a limited number of places)
2. A sign indicating or representing something important or secret:
   2.1. Substitution of a sensitive data element (in cybersecurity)
   2.2. Semi or Non-Fungible Tokens representing ownership rights for some digital or physical assets
   
3. Access tokens:
   3.1. Physical security devices
   3.2. Cryptographic authentication objects
   
4. Lexical token:
   4.1. A natural language distinctive element
   4.2. A programming language unit
   

Summarizing all the above, a token is a physical or cryptographic distinctive representation of or a unique access key to some valuable assets.