From Wikipedia:
A stress fracture is one type of incomplete fracture in bones. It is caused by "unusual or repeated stress"[1] This is in contrast to other types of fractures, which are usually characterized by a solitary, severe impact.
It could be described as a very small sliver or crack in the bone;[2] this is why it is sometimes dubbed "hairline fracture". It typically occurs in weight-bearing bones, such as the tibia (bone of the lower leg) and metatarsals (bones of the foot).
It is a common sports injury, and most cases are associated with athletics.
Recovery-wise, I guess a 2-3 weeks time period to stay off of it and let it heal is typical.