Use the word marginal when something is minimal or barely enough. If you buy lemons and sugar, make lemonade and set up a stand on the street corner, but sell only a couple of glasses, your profits will be marginal.
Some claim that greenhouse gases have a marginal effect on the environment while others think that they are changing the world drastically. Your parents hope to see more than a marginal improvement in your grades! These are the figurative uses for marginal, which comes from the Latin word margo "edge." Literally, the word is used with things on a border. When you scribble words in the blank edges of your textbook pages, those notes are marginal.