ET patch is a packet containing additional files for Enemy Territory. ET servers are using different version of ET patches, so using these you will be able to connect to those servers. Note that you can still use the ET Starter Pro to connect to different ET servers without having to select manually the ET Patch version.
For Windows only:
et_patch_2.60b.zip | Ver. 2.60b [NEWEST VERSION] | Size: 943.06 KB
et_patch_2.60.zip | Ver. 2.60 | Size: 5.53 MB
et_patch_1.02.zip | Ver. 1.02 | Size: 3.23 MB