Definition - What does Secure Delete mean?
Secure delete is a process of data deletion that ensures that the deleted file cannot be retrieved. This process is very important for protecting sensitive data properly, as it removes any way for outsiders to mine discarded storage hardware for data. Secure delete can be achieved in many ways, and a number of software applications have been developed that claim to have this functionality.
Techopedia explains Secure Delete
Secure delete is a way to ensure that the data in its present form is completely gone from the storage device. In contrast, deleting a file in Windows simply moves it to the Recycle Bin, and even if you empty the Recycle Bin or bypass it entirely by using the shortcut key Shift+Delete on a file, the file is not really gone from the hard disk; the OS is simply told that the area where the file was located is free to be used for storing other files. But until that happens, the file still exists in the original disk sectors it was written in. The file will stay there until another file is written over it or the drive gets formatted.
A secure delete application or utility does not simply tell the OS that the space is available, but it also overwrites the location with a meaningless file. This ensures that the physical location of the deleted files has been overwritten. To ensure that the data is truly gone, the secure delete utility must overwrite the file multiple times.