Strumming is a technique that sounds several strings together with down and up motions on a guitar to play a chord. It creates the sound of the chord and the rhythm at the same time and is the foundation of accompaniment.
The basic idea
Combining downstrokes and upstrokes lets you create many different grooves from the same chord progression. Keeping the arm moving even on strokes you do not sound makes it easier to hold the timing.
Using it in performance and programming
Start in 4/4 playing only the downbeats, then add upstrokes on the offbeats and compare. In a DAW you can get close by varying chord length and velocity.
How it differs from related terms
Strumming sounds a chord all together, while an arpeggio sounds the notes of a chord one after another.
Whether you sound all the strings or select just the low or the high ones also changes the role of the accompaniment.
