the physical area which is occupied by a braille character 

any one of the 64 distinct patterns of six dots, including

the space, which can be expressed in braille 

one or more consecutive braille characters comprising a unit, consisting of a root on its own or a root preceded by one or more prefixes (also referred to as braille symbol) 

a blank cell, or the blank margin at the beginning and end of a braille line 

used interchangeably with braille sign