In my (very short, many years ago) stint as an EE it meant that parts (transistors, ICs, etc.) were guaranteed to work within certain specs within certain opera

In my (very short, many years ago) stint as an EE it meant that parts (transistors, ICs, etc.) were guaranteed to work within certain specs within certain operating conditions (temp, etc.). It did not guarantee anything outside of that. Soundness of design and ensuring inputs and environmental factors conformed to the spec was up to the engineers.