don't have any jargon for it but:

play counter melodies to the tune, harmonise using thirds and sixths, also use drones in fifths and sometimes others to complement tune.

You can use a lot of two string chords (three if you are super=flexible).

You can 'shuffle' to the rythm or provide other types of rythmic accompaniment - whatever you 'hear' that sounds good, do it.

Cheers Sarah