A presidium (plural: presidia) is an executive committee with the powers of a larger legislative/governing body, acting on behalf of this body when it is not in session. The term was coined in communist countries around 1920. The Presidium of the Supreme Soviet was headed by the President.
The Russian term is prezidium, and it originates from the Latin term praesidium, that has also led to the English term presidio, both meaning garrison. | 
