A string of x zero bits. For example, 05 = 00000.
Sources:
NIST SP 800-106
The prefix to a bit string that is represented in hexadecimal characters.
Sources:
NIST SP 800-38C
The marker for the beginning of a hexadecimal representation of a bit string.
Sources:
NIST SP 800-38F
A string of x zero bits.
Sources:
NIST SP 800-90A Rev. 1