Deletion Is Often Just a Second Chance
On most computers and phones, dragging a file to the trash does not actually erase it. It moves it into a special holding area called the Recycle Bin, Trash, or something similar. The file still exists, still takes up storage, and can be restored with a single click if you change your mind. The space is only really released when you empty that bin.
Marked, Not Erased
Even after you empty the bin, something interesting happens — or rather, does not happen. The system usually does not bother to wipe the bytes of the deleted file off the storage. Instead, it just updates an internal index to say "the space where that file used to be is now free for reuse." Until something new is written over that area, the original data is technically still there. That is exactly why recovery tools can sometimes bring back files that seem long gone.
Why Storage Can Still Feel Full
There is one more reason space does not always free up the way you expect. Even after files are gone, devices keep many other things around: caches from apps, temporary files, system updates downloaded for later, and reserved areas the operating system uses internally. So even with no obvious files left, a device can still show plenty of storage in use — which is why "deleting" alone does not always make as much room as you hoped.
Source
This article was written using information from Wikipedia.