What's the meaning of "NF","unknown"

[loganzhang1]

Hello,
Can you tell me the meanings of "NF" and "unkonwn" in fer2013new.csv ?

Thanks.

[AlbertoCasasOrtiz]

If I am not wrong, NF stands for "Not a Face," while "unknown" indicates that the emotion is unidentifiable or, at the very least, not one of the emotions present in the dataset.