A coulis is a puree of fruit or vegetables, used as a sauce or flavoring agent to other sauces or soups. As sauces, they are thinned down just enough to reach the proper consistency, but not so much as to alter the intense flavor of the puree.
The word Coulis originally came from the Latin word colare (to strain)
Ayto descrbed it very well in 1993.
A coulis is a thin puree or seived sauce made typically of vegetables or fruit (as Kimmie defined) Nouvelle cuisiners' penchant for using fruit coilis, especially made from raspberries, at every oppurtunity has recently made the term familar to the English speakers, but in fact it had first crossed the channel nearly 600 years ago, in the form of"cullis".This was a sort of strained broth or gravy made originally probably from chicken, but subsequently from any meat or even fish, and used as the basis for sauces or simply poured over the meat dishes.