To wipe a hard drive means to completely erase the drive of all information. Deleting everything does not wipe a hard drive and formatting does not [always] wipe a hard drive. You’ll need to take an extra step to wipe the hard drive completely.
When you format a hard drive or delete a partition, you’re usually only deleting the file system, making the data invisible but not gone. A file recovery program or special hardware can easily recover the information.
If you want to make sure that your private information is gone forever, you’ll need to wipe the hard drive using special tools.