passive

1. Not actively participating in an activity by choice, such as a passive or sleeping partner.

2. Substance rendered inactive, inert, or unreactive through passivation.

3. Device (such as transponder) that only reflects a signal, or transmits a signal only upon receiving a command.

4. Component (such as a cable or pipe) or device (such as a heat exchanger or radiator) that has no moving parts and requires no energy input to perform its function. Also called passive component.