Pertaining to, or kept in, the lower case; -- used to denote the small letters, in distinction from capitals and small capitals; as, lowercase letters a and b and c etc.. Contrasted with uppercase. See the Note under 1st Case, n., 3.
As opposed to Uppercase, Lowercase letters take the form of a,b,c instead of A,B,C. Programs that are 'case-sensitive' can differentiate between upper and lowercase.