There are in fact six main types of spots:
These are small black or yellowish bumps on the skin. The black colouring is not dirt, but rather due to the inner lining of the hair follicle producing pigmentation.
These look similar to blackheads but they can be firmer and when squeezed they will not empty.
These are tender bumps that are red in appearance.
These are similar to papules, but the tip is white in the centre due to a build-up of pus.
Large hard lumps that build up beneath the surface of the skin and can be painful.
Large pus-filled lumps that look similar to boils. These are the most severe type of acne spot and have the greatest risk of causing permanent scarring.