O means Object
N means Normal
X = Horizontal axis
Matches object's Origin with first referenced vertex, then aligns its Normal and (X) Horizontal plane axis toward vertex/along line.
If they are translated differently, maybe it's a mistake. I haven't checked the French translation.
Frenet is the name of a French mathematician. It should not be translated. I linked the wikipedia page of the Frenet-Serret formulas he of which he was the coauthor, and which the Frenet setting refers to.
https://en.wikipedia.org/wiki/Jean_Fr%C ... ric_Frenet
https://it.wikipedia.org/wiki/Jean_Fr%C ... ric_Frenet