the other party; the other side
Refers to the person or group one is dealing with in a transaction, negotiation, or correspondence. Often used in business contexts.
Let's decide the schedule after asking about the other party's convenience.
We sent the contract to the other party.
Compound of 先 (saki, 'ahead' or 'the other side') and 様 (sama, honorific suffix). The reading さきさま is a straightforward combination of the two components.