Resid is a very broad term used to refer to a range of intermediate streams and finished petroleum products.

Intermediates referred to as resid are generally the bottoms from distillation units:

Atmospheric resid - the bottoms from the atmospheric distillation tower

Vacuum resid (VR) - bottoms from the atmospheric distillation and typically the heaviest intermediate stream in the refinery

The finished product typically referred to as resid is heavy fuel oil.