What does the term "Speed" mean in a speaker?

Speed as a function...

Small floorstander, Castle Conway III, intel Nuc, Benchmark Dac pre, Mystere PA, you want ‘speed’, transient attack, dynamics with decay, openness?  Try Captains Audio Envy cables.  I’ve a pr. of the Studio Prestige rca, a usb, & a balanced cable.  Remarkable spacious detailed resolution, the fastest cable I’ve heard.  Lightweight, easy to handle, affordable, speed.   

Example... the Castles r bottom ported adjustable thru spacers to various room sizes.  With AE interconnects, ports wide open, they sound like sealed boxes, absolutely no overhang, spacious, neutral, dynamic, textured speed unleashed thru the speakers carbon fiber drivers.

Addictive.

Same thru a pr. of 1SC’s.  AE interconnects r FAST, and one can easily appreciate such thru the additional frequency range moving beyond the monitors.  Fun too.  Refined, cohesive, spacious, they convey a distinct ‘house sound’ that reminds of a good modern tube amp, or a great set of headphones, the small Castles sound like lovely dark electrostatics with better dynamics.  
Speed indeed...

regismc, a fast cable? Please don't make me choke on my dinner. Electricity travels at the speed of light. All wires have exactly the same speed. Resistance and capacitance are separate issues. Personally, I would rather be addicted to sex. (Big smiles from the wife)

 As much as I have enjoyed reading through this thread, I couldn't help but remember when Velodyne made subs that used an accelerometer on the woofer cone, allowing it to be 'corrected' by the sub amp 3,500 times per second (maybe that is the way they still operate, dunno). It has been a very long time since I have owned such an animal, but I still remember the speed that I heard in the bass. To me, it came across not only in impact, but pitch definition as well. 
 Years earlier, when I owned a pair of corner horns, the bass had much of this kind of quality too, IIRC. 
 The sub that I am using presently (10" driver with a 12" passive radiator) with a velodyne SMS-1, doesn't have these effects, even though the bass is enhanced (increased).

By the way, horns use conventional drivers so they are probably the same.

surroundings which hold cone and magnets(alcinico,neodium) usually is different

The TS parameters for bass driver being used in a horn is very different from the same sized driver used elsewhere. For example, the surround of the driver is much stiffer (typically a cloth material), since the cone moves very little. +/- 1/16 was amount stated in the horns that I made.