All of them feed on dead and decaying matter (detritus). Detrivores and decomposers are distinct, as it says on Wikipedia, in the fact detrivores consume macroscopic clumps of detritus while decomposers metabolise detritus on a microscopic scale. Are detrivores and decomposers both types of saprotrophs? Also, what exactly does the term "saprozoic" mean, and how is it distinct from saprotroph and decomposer?
Saprotrophs feed on dead organic matter by the means of extracellular digestion.
Saprozoic organisms are protozoans that are saprotrophs. This actually comes from an obsolete classification of plants and animals where bacteria and fungi were grouped with plants and were therefore called saprophytes if they are saprotrophic. Protozoans were considered animals; so saprozoic.
Decomposer is a broad class including both detritivores and saprotrophs.
Scavengers also consume dead organisms. They are distinct from detritivores because the former consumes a relatively larger amount of dead matter. Often, scavengers are the first to consume dead organisms; the leftovers are processed by decomposers.
I could not find any authoritative source for these definitions. A peer-reviewed article by Getz (2010) attempts to classify organisms based on their eating habits.
Decomposers are responsible for the "decay" of dead organisms (carcasses), dropped plant matter, and animal wastes (fecal matter) by externally breaking down the organic material and then absorbing the resulting "nutrients." This typifies the approaches taken by many fungi and bacteria. Detrivores actually feed on or consume decaying material, including the decomposers themselves, and/or other detrivores.