Oh good for us.
This is an example of a transmission mount.
A bad one will typically have all the rubber be worn off so that the bolt to the metal bracket that goes to your engine is just loose, hence why it "bangs" when you stop fast or accelerate.
Google your car model+ engine mount/transmission mount to see what yours look like, it should be fairly obvious though. There are usually two on the sides of the engine bay and one+ underneath.