The PHP development team has released an updated version of PHP. PHP 5.3.2 contains a number of bugfixes and some security improvements.
For a full list of changes, be sure to check out their changelog.
This is the 3rd release of the PHP 5.3 series, so expect that web hosts will begin to upgrade their servers. Depending on the type of hosting account you have, the server you are using may be upgraded and begin using the new version, or you may be given the option of which version of PHP to use for your site.