just got back to this thread... sorry....
In general terms, a speaker is "any electromechanical Transducer" that converts energy to sound. Think of it this way. the magnet is, well, a magnet with + and - magnetic poles... now, when you run a current through the voicecoil it acts to attract or repel against the magnetic force(s) in play here. (basic stuff)
There is much to say but I am going to do my best to keep it short.... (ya-rly)
A LOUDSPEAKER, well, the terminology is old and not really used anymore/today, refers to a device, such as the a-fore-mentioned electromagnetic transducer, that is capable of a "LOUD(er)" output than conventional speakers/configrations...in 'the day' of course. (go to any county fair...those metal looking horns you see for the address/pa system... same thing)
Today, the term loudspeaker is usually referenced to as in a public address (PA) system. And is usually a mid to full range device(s) with either a singular "driver" or multiple drivers (hence full range) in a cabinet (or horn) designed to "project" the sound. (ever seen the 'Stacks' of speakers at a concert? - The horn like shape is acoustically designed for hi , read LOUD, output)
Don't be lazy... actually sit down and read the ENTIRE article in Wiki... I think it is very well written and gives a history of the design and evolution of speakers (of all kinds.)