When a the user begins typing a value into a Managed Metadata field, it displays all terms in the associated term set that begin with the characters the user has typed.
This is useful to users who may not be familiar with the terms that are available.
Your instance automatically has access to the metadata server API without any additional authorization.
The metadata server is particularly useful when used in combination with startup and shutdown scripts because you can use the metadata server to programmatically get unique information about an instance, without additional authorization.
If you map the column to an individual term within a term set, then the column will display that term, and any terms underneath it in the hierarchy.
You can create a Managed Metadata column that maps to an existing term set or term at any level on a site (for example, as a site column, or as a column local to a specific list or library).