What is open F tuning (In guitar)?

Question

I have a conflict in information; According to a tuner, open F is (from high to low) FCFAF. Why there is a string missing, I don't know. On one website, open F is almost the same, FCFCAF. (Not sure if the same C is repeated.) Finally, on another website, open F is CFCFAF.

Which is ACTUALLY open F, and how does one tune to it from standard tuning?

Answer 1

from thickest to thinnest stings:


C, F, C, F, A, C

Answer 2

From thickest to thinest Open F is:
FACFCF