These headphones hush ambient noise by creating anti-noise that obviates the noise at your ear. They don't eliminate the outside world, but the better models significantly reduce the whoosh of airplanes' air-conditioning systems. Noise-canceling headphones come in all forms, from full-size to earbuds. Since you no longer have to crank up the volume to overcome background noise, this type of headphone lets you listen at lower levels, which leads to reduced ear fatigue. You'll also hear more low-level detail in your music.
Earbuds have small speakers that rest on the ear canal of the wearer. These are usually much less expensive than on-ear and over-ear headphones and reproduce the sound well. However, outside sounds, such as traffic or power tools, can get past the earbuds and interfere with your enjoyment. Earbuds also don't stay in place very well if the wearer is moving much, such as exercising. These also are lower fidelity than on-ear and over-ear headphones.