In the SQL:2003 standard, access to the data dictionary (or database metadata) is provided by a structure called information_schema. Beacause this is part of the standard and already exists in other database systems, the decision to implement this feature into MySQL was a very good one.
Note
MySQL has added some information that is not part of the standard, for example INFORMATION_SCHEMA.COLUMNS.COLUMN_TYPE. Beware of that fact if you plan to use this information in a software project that has to remain portable to other SQL implementations.
A phpMyAdmin user sees information_schema as a normal database containing views that describe many aspects of the structure of the databases hosted on this server. Here is a subset of what can be seen (and in fact, the only possible operation on this database is SELECT).
Internally, phpMyAdmin calls information_schema for some of its operations, instead of the corresponding SHOW statements to retrieve metadata. However, phpMyAdmin...