Albert Barnes Commentary Exodus 13:20

"And they took their journey from Succoth, and encamped in Etham, in the edge of the wilderness." — Exodus 13:20 (ASV)

Etham - The house or “sanctuary of Tum” (the Sun God worshipped especially by that name in Lower Egypt), was in the immediate vicinity of Heliopolis, called by the Egyptians the fortress of Zar, or Zalu (that is, of foreigners); the frontier city where the Pharaohs of the 18th dynasty reviewed their forces when about to enter upon a campaign on Syria. The name Pithom has precisely the same meaning as Etham, and may possibly be identified with it.