Mahdieh is correct that they are all synonyms. I would have said that "delicious" is more formal than "tasty. " I think "delicious" is also a little bit stronger word in expressing how good the food is. So I would likely either say, "This is delicious" or "This is very tasty!" Really, either would be appropriate in more formal settings in the U.S. For an even more formal and stronger word, you could use "delectable." "Yummy" is the first word little children learn for something they like to eat. In the preschooler show Daniel Tiger, the little cat character says food is "Yum, yum, yummy to my tum, tum, tummy!" But people in the U.S. also use it casually between good friends. For example, if a friend brings some homemade cookies to my house, I would feel perfectly comfortable saying, "Looks yummy!" But I wouldn't feel comfortable using the word "yummy" in a job interview or a banquet.

Mahdieh is correct that they are all synonyms. I would have said that "delicious" is more formal than "tasty. " I think "delicious" is also a little bit stronger word in expressing how good the food is. So I would likely either say, "This is delicious" or "This is very tasty!" Really, either would be appropriate in more formal settings in the U.S. For an even more formal and stronger word, you could use "delectable." "Yummy" is the first word little children learn for something they like to eat. In the preschooler show Daniel Tiger, the little cat character says food is "Yum, yum, yummy to my tum, tum, tummy!" But people in the U.S. also use it casually between good friends. For example, if a friend brings some homemade cookies to my house, I would feel perfectly comfortable saying, "Looks yummy!" But I wouldn't feel comfortable using the word "yummy" in a job interview or a banquet.

Hello :) they are synonyms . the difference is the level of formality . tasty is the most formal one, then delicious , and yummy which most informal one among these three .