David's

In written English, shortening the word "is" to an apostrophe and a letter 's' in this way is very informal and, in general, confined to reported speech and dialogue in works of fiction, and informal notes and personal letters. A person might write "David's coming to visit next week" in an informal note or letter to a friend.

Writing "is" out in full is more formal and more likely to be acceptable in all cases.

Similarly with

I'm / I am
You're / you are (NEVER confuse "you're" with "your"!)
He's / He is
We're / we are
They're / They are (NEVER confuse "they're" with "their" or "there"!)
It's / it is (NEVER confuse "it's" with "its"!)

There may be more but I can't (cannot) think of any at the moment...

Also...

'll for "will"
David'll be home soon

'd for "had"
John'd seen many cars pass by

also - confusingly - 'd for "would"
I'd love a drink!

've for "have"

I should've seen the car coming!
I would've been sad if I'd missed you!

n't for "not" (appended to word) (word sometimes shortened, sometimes not)

You needn't run
You shouldn't run
You haven't spoken

Sometimes combined (More UK than US usage I think)

You mightn't've seen this (You might not have seen this)

You wouldn't've liked the film (you would not have liked the film)


These are informal also.

Thanks, Contrex, for the detailed reply.