When teaching ecology and trophic relationships, I always make a point of distinguishing between scavengers and decomposers because a cursory definition such as "eating dead material" doesn't sufficiently explain the differences between them.
Decomposers have an ecological role specifically filled by bacteria and fungi. They are capable of eating, or at least breaking down, dead material that cannot be eaten by anything else. They speed up the natural process of decomposition simply by splitting up dead organisms into smaller pieces, thereby increasing the surface area of the dead material and making it easier for natural forces to act upon it.
Scavenging is just a particular lifestyle for consumers; all scavengers are consumers, just as all decomposers are consumers. All decomposers are scavengers, but not all scavengers are decomposers. For example, vultures are scavengers because they eat carcasses that have already died of natural causes or been killed by another animal; they behave exactly as a predator would, except they don't do the killing themselves. They are not decomposers, though. Another way of looking at it is that decomposers are generally much smaller, consume less overall energy, are incapable of directly killing their food, and exist on the periphery of the food web, whereas scavengers are the opposite. There are, of course, exceptions.
Two good examples of scavengers are hyenas and jackals. Both animals are actually omnivores, and scavenging may simply be an opportunistic way for them to consume, allowing greater access and flexibility in a variety of ecological environments. Since they are omnivores, they have multiple positions in the food chain, including primary, secondary and perhaps even tertiary consumer positions, although omnivores are often just categorized as secondary consumers to make things simpler.
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