A checksum is a cryptographic hash function (like MD5 or SHA-256) used to verify the integrity of files. When downloading files from the internet, websites often provide the checksum value of the file so that users can ensure the file was not altered during download or corrupted. The user can generate the checksum on their local system and compare it to the one provided by the site. If they match, the file is intact and safe to use. Other options like BitLocker or FileVault are encryption tools, and a password manager is irrelevant to file verification. References: CompTIA A+ 220-1102 Domain 3.5: File Integrity Checking (CompTIA) (ProfMesser)