The term dither fish refers to an arbitrary group of aquarium fish used by cichlid keeping aquarists to reduce innate timidity in some species of cichlids (Barlow, 1967). The technique relies on the ability of cichlids in an aquarium to use the behaviour of other fish species as a measure of environmental security (Loiselle, 1979). Good dither fish are typically schooling species such as Danio spp., barbs and some tetra species.
That would technically be a "target" fish.The theory is that when the larger fish see the small fish swimming out in the open of the tank it draws them out because they see that there is nothing to fear when out in the open. It can also curb aggression in a tank by causing the feuding fish to focus on the dithers rather then fighting amongst themselves.
I have used danios and I'm planning on trying some rainbows because they are larger and my danios became a snack once my other fish got large enough to eat them. So the type of dither will depend on the size of the fish you will use the dithers for.
That would technically be a "target" fish.