After reviewing my classmates defintions, I noticed a lot of similarities.  You can tell that the other posts were done by math teachers.  The words used were more formal using specific mathematical terms.  I would have added a visual to help student’s see the image.  I did try to but I could not download the image for some reason – it was a balance under the equation term.  

I would ask students for their definition first, as an introduction and then, we as a class would work on improving the definition.  I would have the students partner up and come up with examples for equations and functions.