the table in Christian churches where communion is given
"The priest placed the consecrated bread and wine on the altar during the morning service."
a raised structure on which gifts or sacrifices to a god are made
"The priest climbed the stone altar to place the offering of bread and wine before the gods."
A table or similar flat-topped structure used for religious rites.
"The priest stood before the ornate altar to perform the ceremony."
In plain English: An altar is a special table used for religious ceremonies where people offer prayers and gifts to their gods.
"The couple stood before the altar to exchange their wedding vows."
Usage: The term altar refers specifically to a physical object, so avoid using it metaphorically to describe abstract concepts like "an altar of justice." In casual conversation, people often confuse the location itself with the ritual performed there; specify whether you mean the table or the ceremony taking place upon it.
The word altar entered English via the Old French and earlier Old English forms of a Latin term meaning "a high burning place." Although it likely shares roots with words for "to burn" or "high," its primary sense has remained consistent as a sacred table used in religious ceremonies.