Basal when used in a medical sense refers to a minimal level that is necessary for health or life. As used by diabetics and health care professionals, it describes a low, continuous dosage of insulin

Insulin

Insulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle....

 (either as a basal rate

Basal rate

In biology, basal rate is the rate of continuous supply of some chemical or process. In the case of diabetes mellitus, it is a low rate of continuous insulin supply needed for such purposes as controlling cellular glucose and amino acid uptake....

 from an insulin pump

Insulin pump

The insulin pump is a medical device used for the administration of insulin in the treatment of diabetes mellitus, also known as continuous subcutaneous insulin infusion therapy.The device includes:...

 or a slow-acting insulin injection) intended to "cover" the glucose

Glucose

Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...

 output of the liver

Liver

The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...

.

This works together with a bolus

Bolus (medicine)

In medicine, a bolus is the administration of a medication, drug or other compound that is given to raise its concentration in blood to an effective level...

of insulin, which is a dosage of insulin intended to "cover" a meal or to make a large glucose level correction.