The terms are describing how much acidity is present in the oil (usually). Virgin oil usually has less than 2%, extra virgin has less than 0.8%. Also I say usually because some areas don’t regulate this label and it could just be marketing, you need to read the label yourself.
This is showing varying degrees of quality in terms of taste since people obviously prefer less acidic ones.
There is also a difference in the processing but I’m not too sure what the technical differences in that sense are.