What is meant by urlencode and urldecode?

urlencode() returns the URL encoded version of the given string. URL coding converts
special characters into % signs followed by two hex digits. For example:
urlencode("10.00%") will return "10%2E00%25". URL encoded strings are safe to be
used as part of URLs.
urldecode() returns the URL decoded version of the given string.

string urlencode(str) - Returns the URL encoded version of the input string. String values
to be used in URL query string need to be URL encoded. In the URL encoded version:
Alphanumeric characters are maintained as is.
Space characters are converted to "+" characters.
Other non-alphanumeric characters are converted "%" followed by two hex digits
representing the converted character.
string urldecode(str) - Returns the original string of the input URL encoded string.
For example:
$discount ="10.00%";
$url = "http://domain.com/submit.php?disc=".urlencode($discount);
echo $url;
You will get "http://domain.com/submit.php?disc=10%2E00%25".