MOT is short for Motile Total, which is the way to express how many sperm cells are moving forward. MOT is counted in millions per millilitre, so MOT20+ means that there are more than 20 million forward-moving sperm cells in a millilitre. A straw of donor sperm used for insemination contains 0.5 millilitres, so a straw of MOT20+ will give you a total of over 10 million sperm cells for insemination. MOT10+ straws contain about half of that. 

You can read more about MOT here: What does MOT stand for?