Definition from Nolo’s Plain-English Law Dictionary
1) The right to occupy or hold property, sometimes only for a set period of time. 2) The right to hold a position indefinitely, absent serious misconduct or inability to perform the duties of the position. For example, federal judges have lifetime tenure, and professors who are granted tenure generally have indefinite job security. 3) The length of time for which a person has held a particular position. For example, "During my tenure on the Board of Directors, the company has doubled in size."