A patch is usually considered to be a minor change to an operating system or application, generally to fix an issue that does not warrant a major upgrade.
An update can be a much larger change to your software that may be accompanied by a change in the version number of your software such as your software reporting that it is now version 9.02 instead of 9.01, but generally speaking an update, patch, or fix are pretty much the same thing. They are changes, or additions to the programming code of your software.
A Hot Fix is slightly different in that they are not generally meant to be installed by all users of a program, only those experiencing trouble do to conflicts with the hardware or other software of their computer system.
Hope this helps.