Letter Y
Yahoo!    Web portal, mail provider, and search engine. See UK Yahoo web page.

YAM       Yet Another Mailer. An E-mail program for Amiga computers.

Yammer    A communication tool on Office 365.

YellowDog A Linux distribution based on RedHat, and Centos.

Youtube   A website for videos by individuals or organisations.

Y2K       Year 2000. Usually referred to bugs to dates that are shorted to 2 digits than
          4 digits and can cause programs to misrepresent the year as something else.
          For example, year 00 can mean 2000 or 1900?!

Y2038     Year 2038 problem that deals with 32-bit time formats that can reset to 0 after year 2038.
          Affects old timestamp values and functions on unix systems.

Yum       Yellowdog Updater Modifed. A command line management tool for RPM (Redhat Package Manager).