The English language is full of words that sound alike and are spelled the same, which can lead to confusion.
Homonym: [noun] each of two or more words having the same spelling or pronunciation but different meanings and origins (e.g. beat (v.) and beat (n.))
Homophone: [noun] each of two or more words having the same pronunciation but different meanings, origins, or spelling (e.g. new and knew)
Homograph: [noun] each of two or more words spelled the same but not necessarily pronounced the same and having different meanings and origins (e.g. does (v.) and does (pl. n.))
The definitions were taken directly from the Oxford English Dictionary Online (and, where possible, from the Canadian version).
So why did I bring up these definitions? Because they can lead to a few types of mistakes, two of them being mondegreens and eggcorns.
Ever listen to a song and hear the wrong lyrics? That is called a mondegreen. You can read about how the term was coined and a few other examples in the mondegreen wikipedia article. There are whole websites dedicated to these, and they're great to read through to see what you, and others, mishear.
Here is an example: Instead of hearing There's a bad moon on the rise from "Bad Moon Rising" by CCR, people think they hear There's a bathroom on the right. Check out here, here and here for more mondegreens.
These are also related to eggcorns, where the word you are writing is replaced by a word or words that sound alike. (The term eggcorn came about when someone tried to write acorn and it came out as egg corn. Read the stories of how it came about on Language Log, a linguistics blog with many contributors.) If you want to see more, visit the Eggcorn Database.
Have fun passing the time!