Translation:An teach tábhairne.
What is the difference between a pub and a tavern in Ireland? In America both would just be synonyms for "bar".
The word "tavern" isn't used in Ireland - a tarvern is something you might read about in a book :-)
We have Pubs, and we have Bars. Largely synonymous, but some pubs will have more than one bar, (sometimes referred to as a lounge bar and a saloon bar, but you don't see those signposted much these days) and you can have a bar in a hotel, for example.
In another exercise, 'tabhairne' was translated as 'tavern', so I thought 'an tabhairne' is enough to mean 'the pub'. Why is 'teach' necessary?
I'm pretty sure that tábhairne isn't used anywhere on Duolingo, except immediately after teach.
Given that nobody in Ireland has used the term "tavern" in about a hundred years, unless they were being ironic or were reading a novel, there really isn't much point in shortening teach tábhairne by dropping the teach - the word tábhairne on it's own doesn't have any particular significance for people, you might as well just go straight to an pub or an beár (which are fairly common terms).