Various terms are employed in relation to hæmorrhage, according to its seat, its origin, the time at which it occurs, and other circumstances.

The term external hæmorrhage is employed when the blood escapes on the surface; when the bleeding takes place into the tissues or into a cavity it is spoken of as internal. The blood may infiltrate the connective tissue, constituting an extravasation of blood; or it may collect in a space or cavity and form a hæmatoma.

The coughing up of blood from the lungs is known as hæmoptysis; vomiting of blood from the stomach, as hæmatemesis; the passage of black-coloured stools due to the presence of blood altered by digestion, as melæna; and the passage of bloody urine, as hæmaturia.

Hæmorrhage is known as arterial, venous, or capillary, according to the nature of the vessel from which it takes place.

In arterial hæmorrhage the blood is bright red in colour, and escapes from the cardiac end of the divided vessel in pulsating jets synchronously with the systole of the heart. In vascular parts—for example the face—both ends of a divided artery bleed freely. The blood flowing from an artery may be dark in colour if the respiration is impeded. When the heart's action is weak and the blood tension low the flow may appear to be continuous and not in jets. The blood from a divided artery at the bottom of a deep wound, escapes on the surface in a steady flow.

Venous bleeding is not pulsatile, but occurs in a continuous stream, which, although both ends of the vessel may bleed, is more copious from the distal end. The blood is dark red under ordinary conditions, but may be purplish, or even black, if the respiration is interfered with. When one of the large veins in the neck is wounded, the effects of respiration produce a rise and fall in the stream which may resemble arterial pulsation.

In capillary hæmorrhage, red blood escapes from numerous points on the surface of the wound in a steady ooze. This form of bleeding is serious in those who are the subjects of hæmophilia.