What is trailing white-space? Can anyone help explain me about this also give me some example?

Trailing white space is characters at the end of a string, that can't be seen when printed like spaces or tabs. consider the two strings

"Dave" and "Dave "

Both would look the same to a user, if they were just printed to the screen.

but they might cause problems...

len("Dave") // 4
len("Dave    ") // 8

"Dave" == "Dave    " // false
"Dave" != "Dave    " // true

It happens usually because of user input mistakes.

I might type my name, hit the space key on accident, then press enter, since I can't see the space key at the end of my input. But because it causes problems it needs to be removed from the end of strings. This is why user input is often "trimmed" which removes all trailing whitespace.