an informal way of saying "the"... As the others have said, it usually reflects a certain dialect. And although people who speak such a dialect *may* not be highly-educated, it does not mean that they are not smart.

'the'. It's sort of-slang, sort-of phonetic writing of strongly accented speech.

It's slang for the word "the", as in "Why the basement?" Some parts of the US say "da". Often, it's a sign that the person speaking is not well educated. But other times it's part of the regional dialect.

Thank you