Well, Pokémorphs have come to mean everal different things. But most times when the term is used, it means the following:
A human and Pokémon mixed and put into one body. It will almost always, without fail, have the base of a human, but have body parts and such from whatever Pokémon they are mixed with. If a human was mixed with an Espeon, for example, they would have purple fur all over their body. They would have a pair of fox-like ears on top of their head, a tail split into two parts and a red jewel on their forehead. They can usually use the attacks this Pokémon has, so this Espeon would be able to use moves like Psybeam and Morning Sun. This would be their permanent form, and they would not be able to change.
These Pokémorphs are usually created in a lab by mixing DNA or by interspecies breeding, so their form is stable and it cannot change. They are usually branded freaks by both humans and Pokémon alike, and are feared and hated.
Of course most people are sick and tired of these characters, and they usually have a cliché story/life/past/personality.
The other types of Pokémorphs are, to my knowledge:
Taken from the Animorph series with the same idea. A human can turn into a Pokémon at will. Sometimes there are certain restrictions, like only being able to turn into one specific Pokémon and so on.
A human infused with a certain Pokémon on a soul level. Similar to First Nation religion, a human can turn into a certain Pokémon. Sometimes can use its attacks while not in Pokémon form, or can become a hybrid.
As mentioned, they are not Power Rangers of the Pokémon World- aka they are not people who wear armor or clothing with ears and tails shaped to look like Pokémon.
This is NOT a Feraligatr Pokémorph.
This IS a full Charizard Pokémorph.
This IS a full Umbreon Pokémorph.
You can tell because they look human but have the attributes of a Pokémon.
We also have these in the real world. Anthros, furries, morphs, they're humans with animal characteristics. An eagle anthro will be covered in feathers, have a beak for a mouth and talons for feet, and either have wings on their back on in place of hands.
You just have to do a wiki of DA search to find your answers.
~Psychic