where STEM stands for Science, Technology, Engineering, Mathematics (+more!).
There is this fantastic blog launched on February 17 2013 by Rachel Levy, where she collects information on grandmothers who did great work in those fields. Rachel explains:
Perhaps, like me, you are tired of hearing people say “how would you explain that to your grandmother?” when they probably mean something like “How would you explain the idea in a clear, compelling way so that people without a technical background can understand you?”
Here’s a similar saying you may have heard: “That’s so easy, my grandmother could understand it.”
I would like to counter the implication that grannies (gender + maternity + age) might not easily pick up on technical/theoretical ideas.
It is not just about women who are literally grandmothers, but it is meant in the figurative sense: any woman old enough to be a grandmother.