Second source
also: alternate part · dual sourcing · multi-sourcing
A qualified alternative supplier or part for a component, so production can continue if the primary source is unavailable, discontinued or repriced.
Single-sourced parts are a supply risk: a factory fire, a shortage, allocation or a price rise at one supplier can stop your line. A second source is a part from a different manufacturer, ideally pin- and function-compatible, that has been validated in your design.
Some components are easy to dual-source (standard passives, common logic, many connectors). Microcontrollers, radios, sensors, displays and custom parts usually are not, and switching can mean firmware and hardware changes plus re-testing and sometimes re-certification.
Design techniques help: footprints that accept two packages, firmware abstraction layers, and preferring parts made by several manufacturers.
Founder takeaway
Identify single-source parts early, decide which of those risks you'll accept, and design in alternates wherever the cost is low.
engineer review pending