A single line, business, or discipline (usually, in financial services) in which an entity specializes or has its core operations. A monoline is an entity that operates in one industry segment, or provides only one distinct product or service.

Examples of monolines include a bank specializing in credit card issuance (broadly, monoline banks) or an insurance firm (monoline insurer) that provides insurance coverage in the form of one product (one line or type of insurance) such as a life insurance company or an insurer that solely provides insurance coverage for investment-grade securities against loss, etc.