Syntax:
RESET SLAVE [ALL]

RESET SLAVE makes the slave forget its replication position in the
master's binary log. This statement is meant to be used for a clean
start: It deletes the master.info and relay-log.info files, all the
relay log files, and starts a new relay log file. To use RESET SLAVE,
the slave replication threads must be stopped (use STOP SLAVE if
necessary).

*Note*:

All relay log files are deleted, even if they have not been completely
executed by the slave SQL thread. (This is a condition likely to exist
on a replication slave if you have issued a STOP SLAVE statement or if
the slave is highly loaded.)

In MySQL 5.5 (unlike the case in MySQL 5.1 and earlier), RESET SLAVE
does not change any replication connection parameters such as master
host, master port, master user, or master password, which are retained
in memory. This means that START SLAVE can be issued without requiring
a CHANGE MASTER TO statement following RESET SLAVE.

Connection parameters are reset if the slave mysqld is shut down
following RESET SLAVE. In MySQL 5.5.16 and later, you can instead use
RESET SLAVE ALL to reset these connection parameters (Bug #11809016).

RESET SLAVE ALL does not clear the IGNORE_SERVER_IDS list set by CHANGE
MASTER TO. This issue is fixed in MySQL 5.7. (Bug #18816897)

If the slave SQL thread was in the middle of replicating temporary
tables when it was stopped, and RESET SLAVE is issued, these replicated
temporary tables are deleted on the slave.

*Note*:

When used on an NDB Cluster replication slave SQL node, RESET SLAVE
clears the mysql.ndb_apply_status table. You should keep in mind when
using this statement that ndb_apply_status uses the NDB storage engine
and so is shared by all SQL nodes attached to the slave cluster.

URL: http://dev.mysql.com/doc/refman/5.5/en/reset-slave.html

