Commonly used in medicine, the word decubitus is used to mean "lying down". It is derived from the Latin

Latin

Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 verb “decumbere” meaning "to lie down".

When medical professionals use this term to describe the position of a patient, they first state the part of the body on which the patient is resting followed by the word "decubitus". For example, the right lateral decubitus would mean that the patient is lying on his or her right side. Another example is angina

Angina

Angina pectoris, commonly known as angina, is chest pain due to ischemia of the heart muscle, generally due to obstruction or spasm of the coronary arteries . Coronary artery disease, the main cause of angina, is due to atherosclerosis of the cardiac arteries...

 decubitus, (chest pain while lying down),

In radiology

Radiology

Radiology is a medical specialty that employs the use of imaging to both diagnose and treat disease visualized within the human body. Radiologists use an array of imaging technologies to diagnose or treat diseases...

, this term implies that the patient is lying down with the X-ray

X-ray

X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

being taken parallel to the horizon.