Types are properties for Temtems and their Techniques. Currently there are twelve different types discovered. Each type has its own strengths and weaknesses. Types also tie in with the Temtem's design. While Temtem can have up to two types, Techniques can only have one. Clicking one of the types below will show you all officialy revealed Temtem of that type. You can find more Temtem with incomplete information here.
Types of Temtem
As stated above, types have their own strengths and weaknesses. When a technique is ineffective against another type it deals half the damage, however when a technique is very effective it doubles the damage. This way you'll have to be smart what technique to use on specific Temtem. Since Temtem can have up to two types it might also be that types can be 0.25x effective when the technique is weak against both of the Temtem its types or 4x effective when the technique is strong against both the Temtem types.