Some people are quick to label any written mistake as a typo. A typo—short for typographical error—is an unintentional misstrike of the keys born out of hasty typing. An example of a typo would be spelling the word the as teh, or typing alll instead of all. Luckily, spell checker will bail you out of these blunders.
On the other hand, if you see a sign that says Banana’s — 49 cents a pound, it’s safe to say that isn’t a typo, but a person who doesn’t know how to construct a plural. Same goes when homophones are confused: Your always welcome here is not a typo, but a sentence written by a someone who doesn’t know any better, or failed to give their writing much thought.