A technique in guitar playing wherein the the upstroke or downstroke used in playing one note is extended to the next string, allowing two notes to be played with the same effort as put into playing one note. Witness the following example notated in tablature:

     v ^ v v ^ v v ^ v
e|---------------------|
b|---------------------|
G|---------------------|        v: downstroke
D|---------------4-5-5-|        ^: upstroke
A|---------4-5-7-------|
E|---3-5-7-------------|

Try playing this a couple times, and then play it melding adjacent downstrokes together. Much more efficient, eh? Of course, you may be able to play it even faster by slurring, but that results in a much different sound that is sometimes undesirable.