An employee's seniority refers to how long they've worked for their company. The longer someone has been working there, the higher their seniority.
When people talk about seniority, it usually comes up when discussing promotions or job security within a company. If an older worker has more seniority than a newer one, that doesn't always mean the old-timer will get the promotion – but it can be a factor in the decision-making process. The idea is that someone with years of experience and dedication to their workplace deserves some consideration when opportunities come up.
A measure of the amount of time a person has been a member of an organization, as compared to other members, and with an eye towards awarding privileges to those who have been members longer.
Example: It's an old-fashioned company, with parking spaces and other perks doled out on the basis of seniority.
