What actually happens when you delete a file?

Deleting a file typically does not erase its contents. The file system removes the directory entry pointing to where the data lives and marks that space as available for reuse, which is fast because it involves changing a small record rather than overwriting potentially gigabytes of data. Until something else is written over those blocks, the original contents remain physically present, which is the basis of the entire data recovery industry and of digital forensics. Emptying the recycle bin performs the same operation with more finality in appearance and none in substance.

Modern storage complicates this in both directions. Solid state drives use wear leveling and write data to different physical locations than the operating system believes, which makes targeted overwriting unreliable, and they use a TRIM command that tells the drive which blocks are unused so it can erase them in the background, which actually makes recovery from SSDs less likely than from spinning disks. Full-disk encryption changes the picture entirely and for the better: if the drive is encrypted, destroying the encryption key renders all data unreadable regardless of whether the bits remain, which is how the secure erase function works on modern phones and computers and why it completes in seconds.

Practical guidance. For a device you are selling, donating, or discarding, use the built-in factory reset on a device with encryption enabled, which is the manufacturer-supported method and is sufficient for consumer purposes on current hardware. On an older unencrypted drive, use a full-disk wipe utility, and for genuinely sensitive material on a drive being retired, physical destruction is the certain answer. Two adjacent points: deleting a file from a cloud-synced folder deletes it across your devices but the provider may retain versions and trash for a defined period, and files deleted from a phone's photo library typically sit in a recently deleted album for around thirty days before actually going, which is a feature worth remembering both when you delete something by accident and when you assume something is gone.