URL encoding stands for encoding certain characters in a URL by replacing them with one or more character triplets that consist of the percent character "%" followed by two hexadecimal digits.
The two hexadecimal digits of the triplet(s) represent the numeric value of the replaced character.
The characters allowed in a URI are either reserved or unreserved. Reserved characters are those characters that sometimes have special meaning, while unreserved characters have no such meaning.
Using percent-encoding, characters which otherwise would not be allowed are represented using allowed characters.