If you are talking about a male 1/4 connector, it has a sliding sleeve or a switch that shorts it out when it's not plugged in. You plug that end into your guitar so when you unplug your guitar from the amp, it doesn't make any noise.
A shorting mono jack, or unbalanced in your case is a 1/4 jack that shorts the input when there is no 1/4 male unbalanced jack plugged into it. This way if you have nothing plugged into it, the output of the device is automatically '0' no matter where the gain is set.
A switching jack is used in a device like a guitar effects pedal. It allows the battery to be disconnected from the load if there is no guitar plugged into it. Helps save batteries and for all those pot heads out there, how many of them could really remember to turn off the damn pedal when there not using it.
I want to plug an external speaker, same impedance, into into a combi amp and disconnect the smaller internal speaker. I'm told I can do it with a shorting jack but my immediate impression is I end up with two speakers in series and double the load. I'm new at this. Can someone point me in the right direction?