Bottom product of atmospheric pressure crude oil distillation column is termed as

In an atmospheric crude oil distillation column, crude oil is heated and separated into fractions according to their boiling ranges.

The lighter fractions such as LPG, naphtha, kerosene, and gas oils vaporize and are withdrawn from different trays in the column.

The material that remains at the bottom after removal of these lighter components is called Reduced crude, because it has been "reduced" in lighter volatile constituents.

This bottom product is also commonly referred to as atmospheric residue, and it consists of high-boiling hydrocarbons that cannot be further distilled at atmospheric pressure without thermal cracking.

Therefore, it is typically sent to a vacuum distillation unit (VDU) for further processing.

Although residuum is a general term for residue, the more precise and standard term used specifically for the atmospheric column bottom product is Reduced crude.