The Greek noun leimma (λεῖμμα) means a remnant, what is left over, the preserved remainder. It appears in Romans 11:5 in Paul's argument for the continuing faithfulness of God toward Israel: "Even so then at this present time also there is a remnant (leimma) according to the election of grace.\” The word derives from leipō (to leave, to remain) and signifies that which God has preserved from a larger whole.
The leimma theology is one of the most important threads in both Testaments. Isaiah's children are named "Shear-jashub" — "a remnant shall return" (Isaiah 7:3). Elijah despaired that he alone was left, and God corrected him: 7,000 remained (1 Kings 19:18) — a leimma. Paul quotes this very Elijah passage in Romans 11:4 to establish that God's covenant faithfulness to Israel was never based on the whole nation but always on a preserved remnant.
The theology of the leimma guards against two errors: (1) Triumphalism — assuming the entire nation/church is faithful. (2) Despair — assuming faithfulness has utterly failed because the visible majority has apostatized. The remnant is always small, always surprising, always preserved by grace not merit. It is the theology of the "narrow way" (Matthew 7:14) expressed in ecclesiology.