Sometimes searchers will misspell keywords or keyword phrases when they query the search engines. Common misspellings are often used in alt tags, keywords, titles, and page names as an optimization strategy to attract these extra hits.
Intentionally making a spelling mistake in meta keywords or meta tags to catch search engine users who also misspell words when searching.
Errors in spelling. You have to take them into consideration when building your keyword list. The reason is that many people type their search phrases with misspellings, but they are still potential targeted traffic for you.