Muktzeh (מוקצה
refers to things that you are not allowed to handle on Shabbat and festivals because handling them could lead someone unwittingly to desecrate the day.
For example, a pencil is muktzeh on Shabbat, since handling a pencil (or pen) might make you unwittingly start writing something. You have no need to handle a pencil except for writing, so why do you need to handle it on Shabbat?
Flashdrives and other electronic devices are considered "muktzeh" on Shabbat, as are animals outside of your house. I've never understood anything to say that a
pet is muktzeh (since it's like one of your family), but it's certainly true that feeding a pet chametz-based pet food during Pesach is a real problem.
(ChavaK, I know you're aware of all of the issues. I just didn't know if other readers would know what muktzeh was.)