As I understand it, you call it a chord when it's three notes. Two notes technically isn't a chord, the term is "a diad".

If you just play diads (eg instead of playing DGF# to give you a D major, or DGF to give you a D minor, you just use the DG, and double up one or both notes, you are playing a D diad, and it isn't either major or minor -and it sounds bloody good too.

If you play a bouzouki tuned Irish style (ADAD or GDAD) you tend to play diads quite a lot.

This is another situation where less is more.