What does a "350" on my vision test result actually mean?

Lens correction: It is most likely the power of the lens correction you require. Either + 3.50 (farsighted, hyperopic) or -3.50(nearsighted or myopic).

350: The number may mean several things. 20/350 may refer to your vision without glasses. -3.50 may be your prescription strength, the degree of myopia or nearsightedness. Ask your eye doctor for more details if you are unsure.