lowercase

In English¹ letters can be either lower-cased (a, b, c) or upper-cased (A, B, C).

If you have a String which potentially contains upper-cased letters, you can get a new String with everything transformed into lower-case using the .toLowerCase() method.

void main() {
    String message = "Happy Valentines Day";

    String lowerCased = message.toLowerCase();
    System.out.println(lowerCased);
}

This does not change the original String in place. It just makes a new String with all lower-case letters.