What is meant by urlencode and urldecode?

Urlencode returns a string in which all non-alphanumeric charecters except -_. have been replace with a perecent (%) sign followed by two hex digits and spaces encoded as plus(+) signs. It is encoded the same way as in application/x-www-form-urlencode media type
urlencode decodes any %##
encoding in the given string.