A "lump sum" refers to a single payment made at one time, rather than in multiple installments. This type of payment is often used in various financial contexts, such as settling debts, making investments, or receiving a payout from a retirement plan like a 401(k). Receiving a lump sum can provide immediate access to funds, allowing for quick financial decisions. However, it also requires careful planning to manage the money effectively, as spending it all at once can lead to financial difficulties in the future.