Palpedia
The Palpedia is where information about Pals are stored in Palworld; and is also the name of a video series that features the numerous Pals that exist in the game.
Overview
The Palpedia is the database for all of the Pals present on The Palpagos Islands. You are able to access it straight away from the menu.
The Palpedia is also used to label the YouTube videos that Pocketpair has released, but they do not share the same numbering as in the game.
You can find a list of all Pals here.
Pal Subspecies
Many Pal subspecies follow a specific naming convention that consists of appending a Latin or a Greek word to the name in order to denote how it differs from the base species.
- Aqua - Latin for "Water", used in the names of
Water-element subspecies. - Botan - Greek word for "Plant" or "Grass", used in the names of
Grass-element subspecies. - Cryst - Likely a shortened form of the word "Crystal" or "Crystallized", used in the names of
Ice-element subspecies. - Ignis - Latin for "Fire", used in the names of
Fire-element subspecies. - Libero - Italian for 'Freed' or 'Unleashed', used in the names of subspecies that retain its typing from their original counterpart.
- Lux - Latin for "Light", used in the names of
Electric-element subspecies. - Noct - Shortened from Latin word "Noctis", meaning "of the night", used in the names of
Dark-element subspecies. - Ryu - Japanese word for "Dragon", used in the names of
Dragon-element subspecies. - Terra - Latin for "Earth", used in the names of
Ground-element subspecies.
Humans
Despite it being considered inhumane to do so, you're able to capture the humans in Palworld. Functionally, Humans have the 
Neutral element.
Monsters
Monsters were first introduced in Tides of Terraria. They are found only within the Sealed Realm of Terraria but can be captured and worked like any other Pal, although they do not show up in the Palpedia.
You can find a list of them here.