Malapropisms are words conspicuously wrongly used. At least, their misuse is conspicuous to those who know better, like academics. The misuse is that one apparently precise word is used instead of another with a similar sound. (They are named after a character in R. B. Sheridan’s comedy The Rivals (1775) called Mrs Malaprop, who regularly, and ignorantly, uses one long word when she means another. Her name comes from a French phrase, mal-à-propos, which means ‘off the point’.) Avoid malapropisms.
Probably every student makes some malapropism, or more than one, in her or his career. The blatant ones will be flaunted round staff offices and websites as examples of the way in which students flout the rules of the English language. (Often, they are pretty funny. To academics.)
For non-native speakers, it is easier to make malapropisms. The spellchecker is very good at making them. BE CAREFUL – especially when it suggests an alternative for a long word. Some of the commoner ones to avoid, if you want not to annoy your teachers, include the following, which you should look up separately – when you need to. They often come in pairs, and I guess that most malapropisms confuse words that have similar sounds. (Mrs Malaprop herself confuses alligator with allegory, when she talks of "an allegory sunning itself by the banks of the Nile.")
Some examples frequently found by academic teachers and other pedants are: aggravate - irritate; blatant; careen - career; flaunt - flout; list - litany (and liturgy); militate - mitigate - litigate; In a moment - momentary - momentarily; you can find more listed by category. There is also a term malaprop devised by H. W. and F.G. Fowler in The King's English, to cover various forms of misuse of words in similar ways, without necessarily being technically malapropisms.