It is a list of free nodes in the memory. It contains unused memory cells and these memory cells can be used in future. It is also known as ‘List of Available Space’ or ‘Free Storage List’ or ‘Free Pool’.
It is used along with linked list. Whenever a new node is to be inserted in the linked list, a free node is taken from the AVAIL List and is inserted in the linked list. Similarly, whenever a node is deleted from the linked list, it is inserted in the AVAIL List. So that it can be used in future.