- Connected Lookup
- Unconnected Lookup
Different types of caches can be used with lookup like static, dynamic, persistent, and shared(The dynamic cache cannot be used while creating an un-connected lookup). Each of these has its own identification. For more details, refer to Informatica Transformation Guide.
Lookup is a passive transformation, and can be used either connected or unconnected. Typically, connected lookup is used when you want to do the lookup for all rows. When you have selective lookup requirements, its normally better to go for unconnected lookup. Unconnected Lookup can be used as if its a function call.
To read more, here is a good article -
What is lookup transformation in informatica? - IT Community