“Morph” is the name given in the Suocéverse to a discrete evolutive stage or to a given Forme; in the first sense it is basically equivalent to the term “stage”.

A morph is “base” or “initial” when it's the initial stage of a Pokémon species, into which no morph evolves; for example Torchic is the initial morph or base stage of the line that includes Torchic, Combusken and Blaziken. A morph is “final” or “latest” when it's the last morph a Pokémon can reach by natural evolution, and that evolves no further via the normal evolution process; for example, Blaziken in the above example.

There are alternative morphs, that can be reached by evolution process that result in a temporary form. These include such elements as Mega Evolution, which uses an external power source to reach a temporary form.

Depending on the environment, there's the possibility that some Morphs are partially suppressed from the normal evolution tree of a Pokémon species. For example, the requirements of training with humans make some species “skip” their base morph when bred in captivity as is the case of Cleffa, requiring incenses or special, stress-free habitats for them to hatch in their normal initial morph.

The article List of Pokémon has a (always in-progress) listing of all the Morphs that exist in the Suocéverse.