As designers, we get a lot of similarly elusive adjectives from clients, as they tell us what they want their sites to be: “The site needs to be ‘cool,’” “It should be ‘exciting,’” “I want it to ‘pop.’” When we ask them to clarify, the answer we get back sounds a lot like “I can’t tell you what it is, but I’ll know it when I see it.”

“Fun” is a particularly difficult concept to define. And we’re starting to hear it a lot more from clients as we design for different contexts of use.

The good news? We all have an idea of what “fun” is. The bad news? The nuances in these ideas—among designers, clients, and most importantly, users—can mean the difference between a successful project and an unsuccessful one.