Aerospace and defence. The specification is DO-254 (Design Assurance for Airborne Electronic Hardware) in the standards register (RTCA, Inc., version DO-254).
This register says what each scheme asks for. It never says that a product, design, company or site meets a scheme: that is the determination of the body that runs the scheme.
Aerospace and defence: conformance attaches to a design flow.
The level scale, validity, test families, applicability by market, the regulations that invoke the scheme and the accredited bodies are for registered members. Registration is free and takes a minute. You come back to this page afterwards.