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?

Newbee,

I think you should have stated that the bridging of the amp
is done by a switch on the amp - and is part of the design
of the amp.

The paucity of your original explanation may have led someone
that is not particularily versed in amps and electronics to
believe that bridging can be done with any old amp.

I applaud Eldartford for his admonition - otherwise someone
could have damaged their stereo gear.

I think that's something that we all have to take into
account when posting on a forum such as this. There's a
real possibility that someone could misinterpret a poorly
written post and do something they may later regret.

Dr. Gregory Greenman
Physicist