What is Alternate Picking?

Alternate picking is an economy of movement guitar playing technique that involves picking twice the guitar string in a single down-up motion. We've heard before that "all that goes up most come down"; the same is true while alternate picking; "all downstrokes are followed by an upstroke". Once a plectrum strikes a string on the downstroke, the plectrum must also strike the string on the upstroke. In essence, doubling the pick count in a single cycle motion of up and down, thus the economy of movement.