Yum is first and foremost a vocalization of a tasty morsel.
Most geeks, however, would immediately think of Yellow Dog Update Manager (YUM). Don't ask where the 'D' went.
Yellow Dog is a flavor of Linux that deals heavily with PPC-type microprocessors. After Apple switched from PPC to Intel CPUs, they stopped pushing OSX development on the older chips. Yellow Dog, shepherded by Terrasoft in Loveland, Colorado, was the perfect OS replacement.
Almost every flavor of Linux creates some wonderful tool that gets adopted by the other development teams, and Yellow Dog's 'must have' application is YUM. The YUM utility allows simplified Linux updates, package installs and dependency checking. By simply typing
yum -update, you can have a quickly updated system. My internal company webservers run on CentOS, which was created as an offshoot of Red Hat Linux. CentOS adapted YUM, and included a simple cron job to update the server every week.
So, whether your mind drifts towards Linux or Twinkies, the thought should be 'yum'.