Dictionary of Biblical Words:
The “building up” of believers on their most holy faith. Any teaching or doctrine that has this tendency is to edification. The opposite to this is “destructive” (that which “pulls down”).
Concise Bible Dictionary:
From οικοδομέω, “to build, to build up.” The same word is used for the building of the Temple at Jerusalem (John 2:20), and by the Lord when He said He would build His assembly (Matt. 16:18). Οἰκοδομή occurs often in the epistles with the exhortation that all things in the church should be done to edification (Rom. 14:19; Rom. 15:2; 1 Cor. 14:3-26; Eph. 4:16,29). The gifts in the church were also for the edifying of the body of Christ (Eph. 4:12); and when things were at their worst Christians were exhorted to be building up themselves on their most holy faith (Jude 20). As a building is increased and strengthened, so the body of Christ is built up by the ministry of the Spirit through the word until all come “unto a perfect man, unto the measure of the stature of the fullness of Christ” (Eph. 4:13).