There is definitely some overlap on our various integrations/solutions.When you say Experience Cloud, I assume you mean the Audience Library interface within Experience Cloud. If that's the case, Audience library is essentially a very limited version of Audience Manager. If you company has a license to Audience Manager you'll actually see traits for any customer attributes uploaded in the Audience Library interface.
I'm the least familiar with Target but from what I can recall you can upload attributes directly to the Target interface or you can share Audience Library attributes with Target. I don't know for sure but I believe the difference there is more in the upload and update frequency in data rather than taking action on the attribute with Target. I could be wrong there though so don't quote me on that part. For example, Audience Library shared traits can be based on Analytics data that gets updated on a regular basis or real-time basis depending on what is setup. I don't believe Target has a way to regularly bring in outside data from its own interface.
Hope this helps. You could also ask specific questions in the Target and Platform communities and you might get a better answer there. The individual solution communities have a lot more people browsing them that specialize in that topic. The overall Experience Cloud community is less active since a lot of practitioners are still very specialized.