About URL-encoding and URL-decoding:

From Wikipedia, the free encyclopedia

Percent-encoding, also known as URL encoding, is a mechanism for encoding information in a Uniform Resource Identifier (URI) under certain circumstances. While this is known as URL encoding it is, in fact, used more generally within the main Uniform Resource Identifier (URI) set, which includes both Uniform Resource Locator (URL) and Uniform Resource Name (URN). As such, it is also used in the preparation of data of the "application/x-www-form-urlencoded" media type, as is often used in email messages and the submission of HTML form data in HTTP requests. The characters in a URI, regardless of how they might be encoded, are taken from a set of unreserved characters for general use, and a smaller set of reserved characters that sometimes have special meaning in certain contexts. These sets and the circumstances under which certain characters from the reserved set have special meaning have changed slightly with each revision of specifications that govern URIs and URI schemes.