Gusset Jackets are characterized by an extension to the sleeve, at the shoulder, that allows for stretching of the arm in any direction, easily, while allowing the jacket to go back to it's initial form.
Raglan Jackets are characterized by an extension from the sleeve to the collar to present a more refined look and feel.
Set-in Sleeves are simple and clean, and connect the sleeve to the jacket right as the shoulder ends.