Flat has many meanings and definitions. As observed indictionaries, flat means: .
lying at full length or spread out upon the ground : prostrate .
utterly ruined or destroy…ed .
resting with a surface against something .
having a continuous horizontal surface .
being or characterized by a horizontal line or tracing withoutpeaks or depressions .
having a relatively smooth or even surface .
arranged or laid out so as to be level or even .
having the major surfaces essentially parallel and distinctlygreater than the minor surfaces .
clearly unmistakable .
not varying : fixed (2) : having no fraction either lacking or in excess : exact (3) ofa frequency response : not varying significantlythroughout its range .
lacking in animation, zest, or vigor : dull .
lacking flavor : tasteless .
lacking effervescence or sparkle < flat gingerale> .
commercially inactive; also : characterized by nosignificant rise or decline from one period to another .
of a tire : lacking air : deflated .
chiefly British of a battery : dead 3c,discharged (MORE)
the body of flat worm is flat,board and long ribbon like. they are mostly parasites and live in the intestine of man and other animals. they are attached to the organd of …host by suckers and suck the digested food the host. Tapeworms are examples of flat worms. (MORE)
Better question: why are there evolutionary niches allowing flat fish to thrive? Three answers, although you shouldn't consider me an authority: 1. Flounders lay flat on the… bottom, and flatness allows them to be less conspicuous. 2. Flatness minimizes shadows on the ocean floor, thus aiding in stealth. 3. In coral reefs, a flat body and a long nose allows fish to get at food inside coral heads. In each of these three scenarios, it's not hard to understand how flatter fish would be more successful -- and therefore more likely to reproduce. (MORE)