Can you explain the difference between a self and non-self guinea pig?

This is a description of their appearance, and is a general term used quite widely in small animal show circles, being applied to mice and rats too as an example.  Self animals are all distinguishable by the fact that their coat consists of a single (or ‘self’) colour, as shown by the one on the right in the group below.
Self guinea pig or non-self
Self cavies (as guinea pigs are better-known in show circles) are also smooth-haired, so that Abyssinians, for example, feature in the non-self division, along with other smooth-haired variants, such as bi-colours or tortoiseshells.  It is also worth noting that the ‘self’ designation applies irrespective of eye colour – both black and pink-eyed whites therefore qualify for this description, as do pink and dark-eyed goldens.