A spicy ingredient to put in your salad
. Known to botany as Eruca vesicaria
; known to most of the English-speaking world as rocket
's excellent writeup there).
If you have some arugula and don't know what to do with it, you can mix it in with other salad greens; Footprints has a very good recipe for an arugula-based Green Salad with Goat Cheese, Walnuts and Hot Onions.