Percent-encoding
From Just Solve the File Format Problem
Percent-encoding is transfer encoding in which certain "unsafe" bytes are replaced by 3-byte escape sequence. The escape sequence is a percent sign (%), followed by two (usually uppercase) hex digits. Sometimes, as a special case, a space character is allowed to be encoded as a single "+" character.
It is primarily used as part of URL encoding, and Form URL encoding.
The term Percent-encoding is actually somewhat ambiguous, and is often conflated with URL encoding.
