noun
plural -tars
[count] a raised place on which sacrifices and gifts are offered in some religions - sometimes used figuratively
a platform or table used as a center of worship in Christian ceremonies and services
led to the altar
If you are led to the altar, you get married.
left at the altar
If you are left at the altar, you do not get married because the person you were going to marry has decided against it at the last moment.
US