From Ancient Greekἀπέλλαι(apéllai) , plural form of apella, from the Greek word ἀπέλλα, which originally meant fold, fence for animals, and the Spartan verb "apellazw", (ἀπελλάζω) which means to assemble.
Hesychius: apellai (ἀπέλλαι), sekoi (σηκοί: folds), ecclesiai (εκκλησίαι: popular assemblies): Nilsson, Vol I, p. 556