Does the disk usage graph indicate amount of space used or load on a disk?

The topic says it all. If the graphic says 10% does it mean I am using 10% of the disk space or is it a measure of load (stress on the disk)?
Thank you for your insights

Space used.

OK. Thanks very much @Dreamer . That is very helpful.

this mean that from the total space of your hard 10% is filed and 90% is available

Got it. Thank you!