Something trochoid moves like this:
animation by Zorgit
If for some reason the animation isn't working on your computer, then a trochoid path is the boing boing boing line followed by a frantic frog.
If you're in Antarctica, where frogs are in short supply, then to see something trochoid all you have to do is stick a bit of chewing gum to the edge of a food can and then roll it along a table.
You can do the same thing by rolling a coin marked with eraser fluid, or by attaching a small piece of paper to the side a car tyre. Do be sure to ask the owner of the car, first.
And, whatever you do, don't stick it on with a pin.
Spot the frippet: something trochoid. This word comes from the Greek trokhos, which means wheel. In this sense trochoid was coined by Gilles de Roberval, who died in 1675.
To make things even easier, anything that can roll or rotate can also be described as trochoid.