The term “patch” can refer to two different things, depending on whether it’s being used as a verb or a noun.
e.g. “This is my favorite patch.”
The more common usage of “patch” is as a noun, which represents a certain configuration of a modular system. It is analagous to a preset on a software instrument. Unlike software instrument presets however, modular synth patches cannot be simply saved and reloaded. If you wish to save a patch, you must write down each of the connections and settings for the system, and recreate it by hand later. Furthermore, imperfections in analog circuitry could cause an identical patch on a different system with the same kinds of modules, from the same manufacturer, to sound different. It could even sound different on your own system the next day! The ephemeral, imperfect nature of hardware synths is part of what makes them so special.
e.g. “Patch a signal to the CV input.”
“Patching” simply means connecting one signal jack to another using a cable.