What does mono "bridged"

That is a method used to convert a stereo amp to a mono amp where the power of the two channels is combined into one.

Not quite. Don't connect both amps up to the same speaker (in parallel) as Newbee's comment suggests! Damage will result.

The term "Bridged" refers to use of a stereo amp as a differential amplifier, where one stereo channel is driven with an inverted signal. Thus, with a signal applied, as one stereo output goes positive, the other one goes negative by the same amount. A speaker connected between the two Hot (red) outputs of the stereo amp will see the amplified signal, with twice the gain of the stereo amps. (The common (black) outputs of the amps are not connected in any way).

Eldartford, Didn't mean to suggest that at all. I was trying to give the simplist of answers possible re the effect of bridging a stereo amp. There were no express or implied instructions about how to do it, when to do it, or how to use one. I was reserving that to a later time. What about my answer causes you to interpert it to mean hooking up multiple amps to one speaker?