What is a lookup table?

What you have there is called a junction table. It is also known as:

• cross-reference table
• bridge table
• join table
• map table
• intersection table
• linking table
• link table

But I've never seen the term "lookup table" used for this purpose.

Pick your battles, but I'd ask for the person to clarify the naming convention seeing that they've suggested using the same convention for one-to-many and many-to-many relationships. Looks like any foreign key relationship means there's a "lookup" table involved.

If that's the naming convention for other databases, then I wouldn't push my luck.

A lookup table is normally a table that acts as a "master list" for something and you use it to look up a business key value (like "Make") in exachange for it's identifier (like the id column) for use in some other table's foreign key column.

Basically, you come in with something to "look up" and exchange it for something else.

The location_quadmap on the otherhand is a bridge table which, as others have already said, is used when you have a many-to-many relationship between two entities. If you call that a lookup table, then I'd say any table could be called a lookup table. Those tables only contain identifiers to other tables so you'd have to first look up the id on the one table, look up the id(s) that match in the bridge table, and then look up the matching row(s) in the 3rd table? Seems to be taking the term a little too far.