A path is a location to a folder or file in a file system of a Operating System, then is a combination of characters and "/"
An absolute path is defined as specifying the location of a file or directory from the root directory(/).
In other words we can say absolute path is a complete path from start of actual filesystem from / directory.
Start at the root directory ( / ) and work down.
Write a slash ( / ) after every directory name (last one is optional)
cat group1.txt
if for example, we use the above line, this commands work only and only if the "group1.txt" exist in the current directory.
If not works, it's not a problem, the file is present somewhere, before restart the new command, you have to know where
the file is saved.
Now, we supposed that you know where your file is saved you can rewrite the command.
cat /home/a1/group1.txt
Now, we suppose that the file is saved into folder a1 in home,
where: /home is the location respect to root, in fact, you have to descend one level
in the file system like above to access your file.
As you can see from the last commands, all the paths started from /directory whis is a root directory for every Unix machines.
Other examples, where all are absolute path
/home/user/Document/group1.txt
/root/data/dev.jpg
/var/log/messages