The axilla (or armpit, underarm, or oxter) is the area on the human body directly under the joint where the arm connects to the shoulder. It also provides the under-arm sweat gland.

Anatomically, the boundaries of the axilla are:

The contents of the axilla include the axillary vein and artery, as well as the brachial plexus, lymph nodes and fat. Axilla is the space between the side of the thorax and the upper arm.

1.Axillary artery and its branches. 2.Axillary vein and its branches. 3.Infraclavicular part of the brachial plexus. 4.Five groups of axillary lymph nodes and the associated lymphatics. 5.The long thoracic and intercostobrachial nerves. 6.Axillary fat and areolar tissue in which the other contents are embedded.

The term "underarm" typically refers to the outer surface of the axilla. However, the terms are sometimes used interchangeably in casual contexts. Colloquially, armpit refers to an object or place which is smelly, greasy, hairy or otherwise undesirable.

The term oxter is most often used in the United Kingdom and the Republic of Ireland. In Northern Ireland "oxter" generally replaces all other names for the armpit.