Tokens in Drupal are a standard formatted placeholder, which can be found inside a string and replaced by a real value extracted from a related object. The format tokens use is type:token, where type is the machine-readable name of a token type (a group of related tokens), and token is the machine-readable name of a token within this group.
The power of the Token API in Drupal is not only given by its flexibility but also by the fact that it is already a popular API. It is flexible because you can define groups, which contain related tokens, linked by the data object that contains their value (for example, a Node object or User object). It is popular because in previous versions of Drupal, it was the contributed module many ...
