- This is team work.
- This is a team work.
Which is correct?
You work or collaborate together with someone is the intended meaning.
If you are referring to the quality of people working together as a team, then say teamwork - one word. But you have to be talking about people and not an activity.
Work as a noun means "a productive activity" or "a result of a productive activity." A person, however, is typically not considered a work (though his/her parents may disagree).
So you can qualify the noun work with the word team to mean something like "a productive activity for the team" or "the result of a productive activity by the team", but this does not really translate to "a quality of people working together as a team."
Idiomatically, no one says "This is a team work" because of possibility of confusion with teamwork. You can say the more common string of words "This is a team effort" to mean that an effort should not be done by one person.
1, This is team work, is most correct, but would only be used in very specific cases.
Great job guys in setting up the reception hall, this is team work! (While pointing to the work just done.)
The noun form of this expression is most often "Team Effort".
We've got an hour to set up the reception hall, let's make this a team effort.
This is team work. (For nouns)
Without including "a" it's similar to say
"This is stackexchange.com" or "This is E entertainment television"
It's correct if we're trying to say that this what we do represents the truly team work (noun)
This is a team work. (for the action of do things together)
Including "a" it's correct if we mean that We do this together, this(action) is a team work, you know why? because we're a team, teams do team work (noun).
I hope it helps!