In a human resources context, turnover, or labour turnover, is the rate at which an employer gains and loses employees. Put simply, it is how long employees tend to stay with a particular company. Turnover is measured for individual companies and for their industry as a whole. If an employer is said to have a high turnover relative to its competitors, it means that employees of said company have a shorter average tenure than those of other companies in the same industry.
Turnover can be defined as either internal or external. Internal turnover occurs when an employee leaves their current position for a different one within the same organization, either through promotion or demotion. External turnover, obviously, is when an employee leaves the company altogether. Both can either positively or negatively affect a company. In either case, the responsibility falls on HR to ensure the vacated position is filled promptly and adequately.
Turnover rates tend to be higher in unskilled fields. Though they still must eat the cost of training, the companies lose relatively less in terms of performance. Unskilled labour is easily replaced. Turnover in skilled labour fields, however, presents a problem. Individuals specialized in a certain field will surely be in high demand, so competition between companies in related industries comes into play. Replacing said individuals without sacrificing a certain level of skill can present a challenge.
High turnover rates often imply employee dissatisfaction and burnout, whether from unsafe or unfair working conditions or lack of support from management. A number of theories exist for this phenomenon, which I intend to address in future write-ups.
Sources:
http://en.wikipedia.org/wiki/Turnover_%28employment%29
http://eh.net/encyclopedia/article/owen.turnover