Originally Posted by Ironfish653

While they are both circles with 'teeth' Sprockets are intended to be connected by a chain or toothed belt; Gears mesh directly with other gears.
Some people may disagree, but if we're talking about bikes, the little ones on the back are usually refered to as 'cogs' or 'sprockets' The big ones on the front are 'chainrings' or 'chainwheels'

You see less 'Triple' (3-ring) cranks these days, since 10- and 11-speed rear cassettes are more and more prevalent. You can have a wider range of ratios to choose from with a x10 in the back, than with say, an x8, and with smaller steps between the ratios. On any bike's drivetrain you will have 'duplicate gears' where more than one combination of front and rear 'gears' produces the same ratio, with the smaller steps of a x10 or x11 cassette, there's even more overlap, so having 3 rings in the front usually provides a lot more overlap in the ranges, while only a few more 'extra low' ratios. (2x 'double' cranks are also easier to set up)
My last road bike with a triple was a 3x8, and the granny gear only gave me 2 more steps from the lowest ratio covered by the middle ring.

Triples, though, are still popluar with touring and trekking riders, for the ability to have some super-low ratios for climbing, especially with a loaded bike.
A lot of these guys, especially who do a lot of loaded touring, run MTB wide-range cassettes for a huge spread of gear ratios to choose from.