What does the acronym BSA stand for and what is it used for?

BSA is bovine serum albumin. 

BSA is considered as an inert protein in that it rarely interferes with a biochemical reaction. In biochemistry and molecular biology, the inert characteristic of BSA allows it to be used to stabilise enzymes by preventing loss of the enzyme through adhesion to plastics such as pipette tips and other plastic consumables that come into contact with the enzyme. BSA is generally used in solution with the enzyme of interest at a final concentration of 0.5 - 1 milligram/millilitre.

There are many commercially available BSA products and most powder forms are sufficient for the use mentioned above.