Information schema provides access to db metadata and provides information about MySQL server such as database or table name, column data types, access privileges, and more. Another term that may be used for this information is the data dictionary and the system catalog.
Information schema is a database in each MySQL instance, where it stores information about all other databases held by MySQL server. The information schema database contains several read-only tables. Because they actually have views, there are no associated files, and you can not set triggers. Also, there is no database directory with that name.
Although you can select Information schema as the default database using the USE statement, you can only read the contents of table, not insert, update, or delete operations on the table.
mysql> select * from information_schema.innodb_trx\G; Empty set (0.06 sec) ERROR: No query specified