This is a potential security issue, you are being redirected to https://csrc.nist.gov.
The length (in bits) of the bit string x. For example, |01100100| = 8.
NIST SP 800-106
The absolute value of x.
NIST SP 800-56B Rev. 2 under │x│
The length of a bit string X in bits.
NIST SP 800-108r1 under |X|