Apellai (Greek: ἀπέλλαι), was a three-day family-festival of the Northwest Greeks similar with the Ionic Apaturia, which was dedicated to Apollo (Doric form:Ἀπέλλων). The fest was spread in Greece by the Dorians as it is proved by the use of the month Apellaios (Ἀπελλαῖος or Ἀπελλαιών in Ionic Tenos), in various Dorian states. 
The word is derived from the Ancient Macedonian word pélla (πέλλα), "stone", (Heshychius) which appears in some toponyms in Greece like Pella (Πέλλα), Pellene (Πελλήνη)   Beekes suggests that the word πέλλα has probably Pre-Greek origin.  The Doric word apella (ἀπέλλα) originally meant wall, enclosure of stones, and later assembly of people within the limits of the square . The word usually appears in plural. Beekes derives the word from the verb ἀπέλλειν , ἀποκλείειν ("shut off from or out from") therefore apella is the "enclosed space, meeting space". Apella was the popular assembly of Sparta, which corresponds to the ecclesia, in other Greek city-states.
When a pubescent was received into the body of grown men, as a grown Kouros (male youth) he became ἀπελλάξ (apellax, "sharer in secret rites") and he could enter the apellai. The apellaia were the offerings made at the initiation of the young men at a meeting of a family group.
Apellaion is the offering of a part of the hair to the god, and corresponds to the Koureion of the Apaturia. Apellaios is the month of these rites, and Apellon is the "megistos kouros" (the great Kouros).
There is evidence for this festival in Epidavros, Olous, Kalchedon, "Heracleia" at Siris, Tauromenion, Chaleion, Lamia, Oeta (Oἳτη (Oetē)), Tolophon, Delphi and also in Ancient Macedonia. The phratry (‘brotherhood’) controlled the access to civic rights. The three-day family-festival included initiation ceremonies, not concerning the state:
It is almost sure that the fest belonged originally to Apollo, because his name is used in the oaths only near Poseidon Phratrios and Zeus Patroοs. In Athens a common epithet of Apollo as family-god is "Apollo Patroos".