MyISAM
MySQL's original storage engine, the default until 2010. Fast, simple and entirely without transactions — which explains both its popularity and its reputation.
Each table is three files on disk: the definition, the data and the indexes. Locking is at whole-table granularity, so a single slow write blocks every reader, and there are no transactions, no crash recovery and no foreign keys. If the server dies mid-write you run REPAIR TABLE and hope. The advantages were real for their time: low overhead, compact indexes and a cached row count that makes an unqualified COUNT(*) instantaneous. Through the 2000s half the web was built on MyISAM because it was the default and nobody gave it a thought. Today there is no reason to choose it — even the system tables have moved to InnoDB.