This is a rather archaic legal term which became specific to leases and would usually follow the tenendum.
The reddendum would be located in old leases starting with the words "yielding and paying" to then refer to the particulars of the lessee's consideration; i.e. rent.
Osborn defines the term as:
"That which is to be paid or rendered; that clause in a lease which specifies the amount of the rent and the time at which it is payable."
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