A checksum is a unique hash that succinctly represents the content of a file. If any data in the file is changed, the generated checksum will also change. Checksums verify that the content you received is the same content that the publisher shared. Checksums prevent someone from tampering with the content and passing it off as the original.
If checksums are provided, take a moment to verify the content of the file you received. Verification is especially important for key software like operating systems.