A/an fracture is where the bone protrudes out of the skin.
closed.
hairline.
shatter.
open.

An open fracture is where the bone protrudes out of the skin. This usually occurs in accidents where collisions cause a massive blow to the body which then causes the bone to break and be displaced from their original positions. This type of fracture needs immediate medical assistance because this might cause a major blood loss to the body which might result to other complications (e.g. infections, further displacements). 

Once an open fracture occurs, a person is suggested to stay in his exact position and not be moved until medical assistance arrives. Open fractures often require major surgeries and they usually take a longer time to recover than hairline fractures because a protrusion to the skin is evident.