A case-sensitive program that expects you to enter all commands in uppercase will not respond correctly if you enter one or more characters in lowercase. It will treat the command RUN differently from run. Programs that do not distinguish between uppercase and lowercase are said to be case-insensitive.
Text sometimes exhibits case sensitivity; that is, words can differ in meaning based on differing use of uppercase and lowercase letters. Words with capital letters do not always have the same meaning when written with lowercase letters. For example, Bill is the first name of former U.S. president William Clinton, who could sign a bill (which is a proposed law that was approved by Congress). And a Polish person can use polish to clean or shine something. In food, the Calorie, with a capital C, is sometimes used to denote 1000 calories of energy.
The opposite term of "case-sensitive" is "case-insensitive".