The Christian discipline of private prayer in a deliberately set-apart place. The biblical anchor is the Lord Jesus's instruction in the Sermon on the Mount: when thou prayest, enter into thy closet, and when thou hast shut thy door, pray to thy Father which is in secret; and thy Father which seeth in secret shall reward thee openly (Matthew 6:6). The Greek tameion refers to an inner room or storage room in the ancient house — a deliberately private space where one could not be seen by others. The Lord Jesus is correcting the public-display prayer of the hypocrites who pray to be seen by men (Matthew 6:5); His positive instruction establishes the substantive practice: private prayer in a deliberately set-apart place where the believer's attention is focused on the Father without the distraction or temptation of others' observation. The Puritan-Reformed tradition treated the prayer closet as essential to vital Christian life: the believer was to maintain a deliberate practice of private prayer in a fixed place at fixed times; many Puritans literally maintained a small closet or set-apart room for the purpose. The patriarchal-Reformed reader recovers the prayer closet as substantive discipline against the modern fragmentation of prayer into vague mental moments throughout the day: a deliberately set-apart place in the home (a small room, an attic, a basement corner, a chair facing the wall); a fixed time (morning is most common); a regular structure (Scripture reading, prayer covering thanksgiving, confession, intercession, supplication); sustained across years. The practice protects the believer's substantive private fellowship with the LORD against the constant interruption of modern life.