Sanitization keeps code clean, removing the "dirty" injections. In HTML and JavaScript, this is accomplished by removing unsafe tags or escaping user input.
What does "sanitization" mean to C?
It's a compiler feature (at least in Clang) that tries to detect memory addresses that are invalid, such as those that are out-of-bounds, or that are still being used after they are freed.
You can enable it with the -fsanitize=address compiler flag. See here for more info.