Bomber aircraft
Bomber aircraft are military airplanes optimized to deliver large volumes of bombs, missiles, mines, etc., to targets. While they may have a capability to fight other airplanes, that detracts from their mission of attacking a surface target.
Throughout the history of aviation, bombers have changed constantly to meet current military requirements. While a Second World War bomber attacking the heartland of Germany needed considerable defensive armor and armament to survive attack by fighters, modern bombers carry no defensive guns, but extensive electronic warfare systems to defeat or hide from enemy radar.
Bomber sizes
At one time, it was quite routine to speak of bombers as light, medium, or heavy, reflecting both their weight and payload. Their weight would, in turn, define the size of runways they would need, and usually their range.
Current bombers all would qualify as "heavy" by past standards. With air refueling, all have intercontinental range, and can carry large bombloads.
Light bomber
Medium bomber
Heavy bomber
Bombing techniques
Before precision-guided munitions, bombers had several ways to attack, and often were designed around the attack mode.