TimThumb.php (also abbreviated as tt.php, tim.php, thumb.php, etc) is a PHP script for resizing images. It’s not WordPress specific, but tons of WordPress themes use it. Inside the main file, timthumb.php, you’ll see a bunch of configuration options. Most people like to use this to configure TimThumb, but they really should create a seperate file called timthumb-config.php, and put those values there. TimThumb checks if that file exists, and if it does, uses those settings instead.
Since we routinely push out TimThumb updates (for security concerns), we overwrite the TimThumb.php file, which overwrites a customers configuration settings. That’s why we strongly encourage a separate TimThimb configuration file.
timthumb.php = script
timthumb-config.php = configuration settings