Literally to build a house (oikos + domeo), extended to mean constructing any structure. Theologically Paul extends it to the building up of the believing community — spiritual construction through teaching, encouragement, and love. 'Edify' in English translations preserves the Latin equivalent of this word.
Paul makes 'edification' (oikodomeo/oikodome) the criterion for evaluating spiritual practices in community: 'Let all things be done for edification' (1 Cor 14:26). The congregation is God's building (oikodomeo), with Christ as the foundation — and each member's contribution must build up rather than tear down. Ephesians 4:12-16 describes the whole body being built up in love as each part does its work. This is not individualistic spirituality but corporate construction toward maturity.