What does it mean that a partition has hash marks on it for Windows 10?
What does it mean when a partition has hash marks on it in Windows?
It indicates that the partition has been selected (also indicated shown by the blue rectangle in the top part of the dialog where a selection is made.).
Here is an example showing the default selection after opening Disk Management:
After selecting "Expansion (F:)":
You can see the diagonal lines have moved.