Baker's is the possessive of baker, used to show ownership or relation to a baker. In UK English, it can also mean the baker's shop, as in going to the baker's for bread.
My greatest strength is common sense. I'm really a standard brand - like Campbell's tomato soup or Baker's chocolate. Katharine Hepburn
Kyle Baker's work is really funny, but it's also got a very clear vision. Bill Sienkiewicz
We saw a knot of others, about a baker's dozen. François Rabelais
My opponent called me a cream puff. Well, I rushed out and got the baker's union to endorse me. Claiborne Pell
The baker's child goes hungry. Turkish Proverb
A baker's dozen. English Proverb