The Scriptures as written in Hebrew distinguish between a rock or a large piece of rock (tsur) and a crag (seʹlaʽ). Both terms are used literally and figuratively in the Scriptures. The two are found in parallel at 2 Samuel 22:2, 3 and Psalm 18:2: “Jehovah is my crag . . . My God is my rock.”

The Bible preserves the names of certain crags and rocks. For example, the Midianite prince Oreb was killed by Gideon’s men at a rock called Oreb, evidently so named because of this incident. (Jg 7:25; Isa 10:26) Mention is made of the crag of Etam, where Samson lived for a time (Jg 15:8), and the toothlike crags of Bozez and Seneh, where Jonathan and his armor-bearer attacked an outpost of the Philistines. (1Sa 14:4, 5) It was at Meribah, in the vicinity of Kadesh (there was another Meribah near Rephidim in the mountainous region of Horeb [Ex 17:7]), that Moses and Aaron were aggravated to the point of failing to sanctify Jehovah in bringing water out of the crag for the assembly.​—Nu 20:11-13; Ps 106:32, 33; see MASSAH; MERIBAH Nos. 1 and 2.

Figurative Use. In a figurative sense “rock” describes the qualities of Jehovah as the Father of Israel (De 32:18), as a stronghold (2Sa 22:32, 33; Isa 17:10), as the secure height and refuge of his people (Ps 62:7; 94:22), and as their salvation (De 32:15; Ps 95:1). Some have looked to false gods as their “rock.” (De 32:37) There are other examples in which “rock” symbolizes in a general way a place of safety, protection, security, and refuge. (Isa 2:10, 19, 21) In Isaiah 8:14 Christ Jesus is alluded to as “a rock” over which “both the houses of Israel” stumbled.​—Compare Mt 21:42-44.

In Jesus’ illustration of the sower, the Greek adjective pe·troʹdes (related to the noun peʹtros) is used to describe the rocky places upon which some of the seed fell. (Mt 13:3-5, 20) Peʹtros is used as a proper name, “Peter.” (Joh 1:42) On the meaning of this term Vine’s Expository Dictionary  of Old and New Testament Words (1981, Vol. 4, p. 76) remarks: “Petros denotes a piece of a rock, a detached stone or boulder, in contrast to petra, a mass of rock.” Word Studies in the New Testament says about peʹtros: “In classical Greek the word means a piece of rock, as in Homer, of Ajax throwing a stone at Hector, . . . or of Patroclus grasping and hiding in his hand a jagged stone.”​—By M. Vincent, 1957, Vol. I, p. 91.

The Greek word tra·khysʹ, which means “rough” (Lu 3:5), refers to jagged, uneven reefy rocks at Acts 27:29.

Another Greek word, spi·lasʹ, evidently has reference to a rock or reef that is hidden beneath the water. It is used by Jude to illustrate certain men who had slipped into the Christian congregation with corrupt motives. As hidden rocks were a menace to ships, so these men constituted a real danger to others in the congregation. He says of such men: “These are the rocks hidden below water in your love feasts while they feast with you.”​—Jude 12.

For a discussion of Matthew 16:18, see ROCK-MASS.