A rooster is a boy chicken of any breed. A fryer, purchased from a hatchery, can be either male or female (often not) of a heavier breed. They're all chickens. (Okay, there are rabbits that are called fryers but I suspect you're talking poultry here.)
The only real difference is how much meat they have on the carcass.
Broilers: 6-8 weeks old and weighing about 2 1/2 pounds
Fryers: 6-8 weeks old and weighing 2 1/2 - 3 1/2 pounds
Roasters: less than 8 months old and weighing 3 1/2 - 5 pounds
Stewing hens: over 10 months old and weighing 5 - 7 pounds
A quick easy way to tell if it should be a roaster, fryer or stewing chicken is to check the bottom of the breastbone, and the more cartilage there is the younger the chicken.
I'm just saying that because sometimes I forget to mark the bags of the processed older chickens so I don't know what I have till it's thawed enough that I can check the cartilage.