What are higher organisms and Lower organisms?
You might have learnt that all organisms are classified according to the complexity in their organisation. The organisms that are simple in their organisation, are placed lower down the order, while those that are complex are placed higher. the term lower organisms refers to the simple organisms while higher organisms refers to complex organisms.
Hope this clears your doubt,
The distinction is typically decided in the domain cognitive sciences, and reserved for organisms with a large mammalian brain and properties of cognitive function. In accord with this "higher and lower" distinction are concepts which refer to specific properties of cognitive function as the important distinction that separates the two groups —among them, concepts such as sentience, sapience, intelligence, cognition, and language faculty.