A relative path is a path that does not start with a root (prefix)
It is relative to another path that is unknown. You need to transform it as absolute|absolute path before accessing any file.
Below is an example of a relative because it does not start with a root (prefix)
joe/foo
Below is an example of an absolute path because it does start with a root (the Linux root)
/joe/foo
Relative file paths are much more portable because they don't depend on the whole path.
Therefore your files can be installed in two different directories. Via a configuration, your application can calculate the two differents absolute path
A relative path is not a file identifier while an absolute path is.
Therefore, it does not identify uniquely a file and needs to be transformed as absolute path.
To get an absolute path from a relative path, you need to concatenate:
By default, the absolute path applied is the working directory (known also as current or default directory).