Definition: A depression caused by erosion by water or ice. Low-lying land bordered by higher ground; especially elongate, relatively large gently sloping depressions of the Earth's surface, commonly situated between two mountains or between ranges of hills or mountains, and often containing a stream with an outlet.
Definition: A heterotroph with a temporary parasitic association with another organism that leads to the death of the host. After which, the parasitoid can continue without the host or can move on to a new host. These organisms are considered partly parasites and partly predators.
