A MIDI connection has 16 virtual channels. This basically means that you can send different MIDI messages to different devices over one cable by setting the sending and receiving units to the same channel.
Patches and banks aren't specific to MIDI, but apply to nearly all types of synthesizers, MIDI or not.
A patch is a like program that configures the various modules inside the synth to produce a certain sound. In the early days, the various modules were physically connected with patch cables. The configuration created by all of the connections taken together was called a patch. In modern synths the connections are made electronically, but we still call them patches. So, a patch basically denotes a single instrument voice. This usually includes the preset instruments as well.
A bank is basically a section of memory containing patches. In the old days, the processor inside the synth could access a very limited number of memory locations. The accessible memory space could be enlarged by switching between several banks of memory. While this is no longer necessary and actually makes for a poor user interface, many modern instruments still use a bank switching scheme.