A path is absolute when it starts with a root (prefix).
It contains all the information needed to locate the file.
Inside a file system, the absolute path is the file identifier.
Absolute path:
/home/username/readme
This is an absolute path because it starts with a forward slash /. This character is the root character on a Linux system.
Relative path:
The below path is a relative path because it does not start with any prefix (root) character
username/readme