Alternatively referred to as a partial path or non-absolute path, a relative path is a URL that only contains a portion of the full path based on it's relation to the directory to which it is linking (there is a simpler explanation below). These shorter addresses are convenient for those who create web pages because they require less typing and take up fewer characters.
How does it work?
We'll use Computer Hope as an example. On our site, we could link "https://www.computerhope.com/jargon/c/cpu.htm" to "https://www.computerhope.com/jargon/m/monitor.htm" only using "../c/cpu.htm" as both the "c" and "m" directories are in the same folder. The "../" portion of the relative path means "go back one directory."