The cryptographic signing of Software to deter tampering.
Signing of software with the X509 or OpenPGP keys by software authors allows checking that the software does indeed come from them. Signing by software distributors (typically LinuxDistributions) allows checking that the software has not been tampered with on mirrors or by third parties.
See also: 
http://aharp.ittns.northwestern.edu/software-sig.html
No other page links to SoftwareSigning yet.
