Q:

What's the term for using the wrong word because it sounds the same?

I was reading about various terms for incorrect words, but they didn't seem to fit.  I saw a post where someone said "what do you like to do when you're board?".  That kind of thing.  Also, would that be considered a mistake in grammar?  I didn't think so, but my friend insists it is.
I'm not sure if there even is a word for that kind of mistake, but was just curious about it.  Thanks!

A:

Actually, a malapropism is the substitution of a word that sounds similar, but not identical, to the intended word (such as when Archie on "All in the Family" referred to the "Women's Lubrication Movement", rather than "Liberation").
In Strahan's example, "bored" and "board" are words that sound identical but are spelled differently. These are called homophones.
As far as I know, Strahan's example would simply be called a misspelling. I don't know of any term that specifically means substituting a homonym. In a case like this, it's irrelevant that "board" also happens to be a word, as its meaning is obviously unrelated to the text.

A:

Malapropism fits the bill I think.
Form oxford:

The mistaken use of a word in place of a similar-sounding one, often
  with an amusing effect (e.g. ‘dance a flamingo’ instead of flamenco).
Origin
Mid 19th century: from the name of the character Mrs Malaprop in
  Sheridan's play The Rivals (1775) + -ism.

EDIT: I know this doesn't seem to satisfy the OP's example of bored/board. But the OP maybe couldn't think of a better example. It satisfies what they asked for in the title: "What's the term for using the wrong word because it sounds the same"

