Final answer:
The structure being described in the question is the subcapsular sinus, which is located in a lymph node.
Step-by-step explanation:
The lymph node acts as a filtering station for lymph, a fluid in the lymphatic system. It contains various components, including a subcapsular sinus which is occupied by dendritic cells, macrophages, and reticular fibers.
The lymph node plays a crucial role in the immune system by trapping and destroying pathogens present in the lymph fluid before it is returned to the heart. Therefore the subcapsular sinus is a structure located in a lymph node and plays a crucial role in filtering lymph fluid.