At some point someone is going to ask you to make something cool. When that happens ask them what ‘cool’ means then watch them mumble and say things like, “You know...cool. Like (fill in the name of a product/band/book/designer/illustrator/etc).”
It’s a ridiculously broad, and bland, term that actually defies meaning unless you know the audience and in whose voice you should be judging cool. It means different things to different people. It's so bland that it substitutes for 'okay' in conversation. What is cool to a gun nut might be very different from what is cool to an 8-year old girl. But you can get more nuanced: What is cool to a gun nut might be different from what is cool to someone into cars. Until you know the audience you won’t understand the term.
And it’s not just ‘cool’. Words like cool, weird, sexy, dark, vintage, etc all need deeper explanation. When a client, partner, collaborator says something needs to be cool (or any other vague descriptor) pause the conversation and drill deeper to find out what they really mean. What does cool mean to them? Cool for what audience? What emotions are embedded in their concept of cool? Can they point to similarly cool projects? Can they use other adjectives that have more specific meaning (daring, provocative, ugly, sleek, dirty, etc)?