Is the expression "What's that mean" correct? [duplicate]

Today I saw a comic where one of the characters say:

What's that mean?

I am not a native English speaker but that sentence puzzled me.

I would personally use the verb to do here but instead there's a 's which I assume is the verb to be contracted.

The other option is that 's here is the verb to do contracted, but I'm not aware of this contraction to be possible.

Is the sentence correct in English? Or is it some "slang" language. The character is not supposed to speak slang or incorrect English at all, so that's why this sentence drew my attention.

Solution 1:

“What's that mean?” is a very informal contraction, typical of speech, of the following

What is that supposed to mean?

From Macmillan Dictionary

used when you are annoyed or offended by something that someone has just said

• A: ‘I just assumed you wouldn’t know.’
  B: ‘Well, what’s that supposed to mean?’