Latin ferlang, ferdingus.
Ferlang and ferdingus are normally translated as furlong in the Phillimore edition though two entries in Hampshire are inconsistently rendered as quarter (NF10,4. IoW1,8).
For more detail, see the note to DEV 1,4 in Domesday Book, vol. 9: Devon, edited by Caroline and Frank Thorn (2 vols., Phillimore, 1985), which can also be found online at: https://hydra.hull.ac.uk/resources/hull:535..