SNTP is an acronym for Simple Network Time Protocol.
SNTP is a less complicated version of Network Time Protocol (one of the oldest still used Internet protocols), which is a protocol for synchronizing clocks of networked computers.
You don’t need such precise time in your single Desktop PC, but especially computers that are connected in a network and are amenable to realtime data sharing need accurate timekeeping to avoid run-time errors and data corruption or loss.
Two or more computers with clocks that are just fractions of a second away can harm your data integrity.
SNTP is a more simple subset of NTP without the high effective filtering mechanims.
It’s often used by embedded systems e.g. for equipment in power substations or industrial environments.
But you can synchronize your SNTP equipment with every NTP time server because a NTP time server is automagically a SNTP time server as well.
The RFC for SNTP can be found here: http://www.faqs.org/rfcs/rfc1361.html
