MySQL is a very fast, multi-threaded, multi-user and robust SQL (Structured Query Language) relational database server. MySQL is Free software. It is licensed under the GNU General Public License.
MySQL didn't have support for transactions for a long time, but it has them now.
MySQL is open source and works on many different platforms including AIX, BSDi, DEC Unix, FreeBSD, HP-UX, Linux, Mac OS X, NetBSD, OpenBSD, OS/2 Warp, SGI Irix, Solaris, SunOS, SCO OpenServer, SCO UnixWare, Tru64 Unix, Windows 95, 98, NT and 2000.
MySQL has C, C++, Eiffel, Java, Perl, PHP, Python, and Tcl APIs.
In case you were wondering MySQL is pronounced My S-Q-L NOT My-Sequel.
In August 2001, a test version of wikipeda using PHP and MySQL appeared, see the Wikipedia PHP script page.
See also: PostgreSQL, Berkeley DB