A key is a tool used to identify or diagnose specific objects or situations. Keys use a process of elimination where the user is presented with a series of choices that describe features of the object. By selecting those choices relevant to the specimen to be identified, those objects that do not match the selected choices are rejected. This allows the rapid elimination of large numbers of objects that the specimen cannot be. The process continues until only one object or a short list of objects remains, identifying the specimen or at least providing a short list of possible identities.

There are two main types of keys:

Dichotomous keys – follow a tree structure. This is the type of key built using Lucid Phoenix

Multi-access keys – where the key is structured in the form of a matrix - the type of key that is built using Lucid3.