The larger veins, called deep veins, give a majority of blood to the heart while superficial veins are found under the skin surface.

Leavitt said Trump noted "mild swelling in his lower legs," which prompted the White House medical team to evaluate him. They concluded that Trump has chronic venous insufficiency -- a condition in which there isn't adequate blood flow in the veins in the legs. This can cause the blood to pool, causing swelling in the lower legs.

The White House released a memo from Trump's physician on Thursday which revealed the president was diagnosed with CVI after he noticed swelling in his legs.