Wikipedia does not currently have an article on "⊑", but our sister project Wiktionary does:

Read the Wiktionary entry on "⊑"

You can also:

• Search for ⊑ in Wikipedia to check for alternative titles or spellings.
• Start the ⊑ article, using the Article Wizard if you wish, or add a request for it; but please remember that Wikipedia is not a dictionary.