Hebrew mizbe'ach haqeṭoret, "altar of incense." A small acacia-wood altar overlaid with gold, 1 cubit square and 2 cubits high (about 18" x 18" x 36"), standing in the Holy Place just in front of the veil that separated the Holy Place from the Holy of Holies (Exodus 30:1-10, 37:25-28). Morning and evening the priest burned a specially-formulated incense (Exodus 30:34-38) on this altar — the incense whose fragrance filled the Holy Place and drifted through the veil into the Holy of Holies, symbolically rising into God's presence.
The altar of incense is the tabernacle's picture of prayer. The incense itself was of four ingredients — stacte, onycha, galbanum, and pure frankincense — in equal measure, specifically forbidden for common use (Exodus 30:37-38). The smoke of incense rising before God parallels the prayers of His people rising before Him, and Scripture makes the connection explicit: Psalm 141:2 — "Let my prayer be counted as incense before you, and the lifting up of my hands as the evening sacrifice"; Revelation 5:8 — "golden bowls full of incense, which are the prayers of the saints"; Revelation 8:3-4 — "another angel came and stood at the altar with a golden censer, and He was given much incense to offer with the prayers of all the saints on the golden altar before the throne, and the smoke of the incense, with the prayers of the saints, rose before God from the hand of the angel." Christian prayer is incense to God. The altar of incense was immediately in front of the veil — as close to God's presence as any priest could be outside the Holy of Holies itself. Prayer is the discipline that brings us nearest to God short of death or the new creation. When Zechariah encountered the angel Gabriel (Luke 1:11), it was at the altar of incense — the angel came at the hour of prayer, in the place of prayer.