Hello. This is my first time answering questions.. I hope this would help you understand.
"아리송하다" is adjective, which means "confusing" , "vague". Here is an example.
" 그 문제는 아리송해요" : "That problem is confusing"
It means you are just not sure if something is right or you just don't remember something.
Also, there is another term "알쏭달쏭하다" , which basically means the same. In my personal view, people tend to use "알쏭달쏭하다" more since it's fun to pronounce.
Have a nice day ^-^