It does not refer to the concept of length.
Here are some examples of words derived from "ped":
* Pedal: the part of a bicycle or other machine that is pressed by the foot
* Pedestrian: a person who walks, especially in a town or city
* Pedicure: a cosmetic treatment for the feet
* Biped: a two-legged animal
* Quadruped: a four-legged animal
While the root "ped" doesn't directly refer to length, some words derived from it can be used in the context of length. For example, you might say "the length of the pedestrian walkway," where "pedestrian" refers to someone who walks, and "walkway" refers to a path of a certain length. However, this is not a direct relationship between "ped" and "length."