The word "starving" technically means that you haven't eaten for days or weeks and your body is in pain from not having enough food. But when people are hungry, they often exaggerate their hunger by saying "I'm starving!"
A: Are you hungry?
B: Yes, I'm starving!
Saying "I'm starving" when you're hungry is casual but can be used in business situations as well as with friends. It's a little more common for men to say than women.