This is the name for a select group of Spartan elders. According to Herodotus (1.67.5: web address 1) five were selected each year from the eldest members of the cavalry, not from the ephors.
[1] Adler called these final three words locus dubius, and capitalized, as here, the word Ephors. For a speculative argument that this phrase should actually read "from the [sc. writings] of Ephoros", see D. Whitehead, 'Ephorus(?) on the Spartan constitution', Classical Quarterly n.s. 55 (2005) 299-301. [The suggestion has been taken up in Brill's New Jacoby s.v. Ephorus, by Victor Parker. However, the evidential basis for it is illusory, according to I.C. Cunningham, CQ n.s. 61 (2011) 312-314.]