The phrase "high altar" refers to the main or central altar in a church or religious building. It holds significant importance and is often located at the front or center of the church. Full definition
From the three - legged dining table on which St. Peter was supposed to have celebrated his first mass in Rome, to the monolithic high altar of St. Peter's Basilica, to the «convenient wooden communion table» prescribed by Archbishop William Laud, the church has wrestled with the alternatives: altar or table? (religion-online.org)
And yet, in the church of each monastery and convent, there was to be found the same high altar dedicated to the Holy Trinity, the same Lady Chapel for the Blessed Mother, and altars and shrines to saints of both sexes. (firstthings.com)
Of particular interest are Michelangelo's Pietà, the bronze statue of St. Peter, and Bernini's canopy over the high altar. (silversea.com)