Generally, a timestamp is the current time of an event that is recorded by a computer. You can use digital timestamps via a trusted authority to certify and protect your intellectual property or your records integrity.
A special form of timestamping is called "trusted timestamping", which is described in RFC 3161. A "trusted timestamp" is a timestamp issued by a trusted third party (TTP) acting as a Time Stamping Authority (TSA). It is used to prove the existence of certain data before a certain point without the possibility that the owner can backdate the timestamps.