What is the type column in MySQL EXPLAIN?

The type column in the MySQL EXPLAIN output describes how a table will be accessed when running the query. You're getting information on whether and how an index is used. Some of these types expose technical implementation details and are, therefore, uninteresting to you.

In most cases, you can't do much to change the access method MySQL has chosen. Any type listed below as bad should be investigated closely to make the query faster. And some of the good ones still have possible performance optimizations specific to their type. Nevertheless, a high percentage of rows loaded with the index and really used (filtered column) is the most important factor - especially as it is the deciding factor for the depends ones whether they are fast or slow.

Performance	Type	Description
good	`const` good	The table is replaced in the query by the row's columns	View
good	`eq_ref` good	A primary/unique key is used to find rows in a join's target table	View
good	`index_subquery` good	An IN(subquery) optimization when returning index values	View
good	`range` good	An index is used to select rows based on a range condition	View
good	`ref` good	Zero or more rows are loaded with an index	View
good	`ref_or_null` good	A nullable condition is utilizing an index	View
good	`unique_subquery` good	An IN(subquery) optimization when returning unique values	View
depends	`fulltext` depends	A full-text search is executed with the associated full-text index	View
depends	`index_merge` depends	Multiple indexes are combined to match the query's filters	View
bad	`ALL` bad	The full table is scanned without using an index	View
bad	`index` bad	An entire index was scanned due to the lack of a better one	View