Byte

A group of eight bits that is treated either as a single entity or as an array of 8 individual bits. 
 
See FIPS 197 for more information. 

A bit string consisting of eight bits. A byte is represented by a hexadecimal string of length two. The right-most hexadecimal character represents the rightmost four bits of the byte, and the left-most hexadecimal character of the byte represents the left-most four bits of the byte. For example, 9d represents the bit string 10011101. 

See the following for more information: 
NIST SP 800-56A Rev. 2 
NIST SP 800-56B Rev. 1 
NIST SP 800-106 
NIST SP 800-38D

A group of eight bits that is treated either as a single entity or as an array of eight individual bits. 

See NIST SP 800-67 Rev. 2 for more information.