There is no difference in meaning between 「おいしい」 and 「うまい」 --- "delicious", "tasty", "yummy", etc. --- but there is a difference in usage and nuance.
「おいしい」 sounds more refined and often more feminine than 「うまい」. 「うまい」 sounds more down-to-earth and intuitive, and it could carry a small amount of light vulgarity.
If you were a Japanese-speaking parent, you would probably not want to hear your little girl use 「うまい」. Even if your kid were a boy, you would still not want him to use it too often until he was, like, out of elementary school. I am actually speaking from my own experience here. I am male so I usually somehow got away with saying 「うまい」 as a kid, but my sister did not. Our mother basically never used the word herself nor did she allow her daughter to use it.
After a few decades, however, more women definitely use 「うまい」 like it was nothing. On TV shows about food, you might hear young women use 「うまい」 almost as often as they use 「おいしい」 these days.