Motor oil derived from traditional hydrocarbon/crude-oil sources (decomposed dinosaurs and plant matter). Also often referred to as "mineral" based oil. This in in contrast to the new synthetic lubricants which have to be "manufactured" from various chemicals rather then just simply boiled off from a crude-oil source. Synthetics are seens as superior to dino oil since the manufacturing process is more controlled and may not require the polymer additives to achieve the same desirable lubricating properties. Synthetics are also more expensive then dino oil.
I justify the extra cost of synthetics over dino oil by going longer intervals between oil changes.