A Digital Rectal Exam (by the way, the word digital here refers to the fingers, not to computer technology) is basically the same as an internal Prostate Massage. This medical prostate exam is often abbreviated as DRE.
In the case of a DRE, the physician (or nurse) will check for overall size, the condition, lumps or certain irregularities of the prostate gland with the fingers to establish if there are prostate health issues, such as excessive prostate enlargement or possible signs of prostate cancer.
Typically, you will lie on your side on a medical treatment table, with the knees bent up towards your chest. The physician will wear a lubricated glove to insert their finger into the rectum, search for the prostate, and will press/feel i.e. palpate along the sides of the prostate.
The doctor may also massage or rub the prostate to obtain fluid for medical analysis to see if there are any inflammations or infections. In official medical terminology this fluid is called Expressed Prostatic Secretion (EPS).
If the prostate is massaged during a DRE (and fluid is subsequently released through the urethra and penis), men generally claim that they feel relief of certain symptoms, such as those connected to Benign Prostate Enlargement.