Syntax:
RESET SLAVE

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.)

If any startup options for setting connection parameters (such as
master host, master port, master user, and master password) are in use,
then any corresponding connection information stored in the master.info
file is immediately reset using the values specified for these options.
Options for which values are not specified are cleared. However, since
these options are deprecated in MySQL 5.1 and removed altogether from
MySQL 5.5, you are encouraged to use a CHANGE MASTER TO statement
instead to reset the connection parameters. (If you do not use the
startup options, you must issue CHANGE MASTER TO in such cases if you
do not want the connection settings to be cleared.)

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.

URL: http://dev.mysql.com/doc/refman/5.1/en/reset-slave.html

