What is case-insensitive?

Question

please some explain what is mean by case-insensitive, here is only how we use it, but actually don't know what is mean by this...

Answer 1

Here is an example two letters in a case-insensitive environment:
A == a

In a case-sensitive environment:
A != a

Answer 2

it's aproperty for alanguage that if you write an identifier or datatype or any thing in code
for example in lower case you must use it in other statements in lower case you can't use it in upper case as it will not be do the job right