Drum is the Constant which we in the process that is always the whole process is nearly dependent (main factor ) ,buffer is the back up (inventory )Which we create to manage the drum ,rope ensures us that the buffer is always maintained ( ensure that inventory is never out of limit ).
Kanban (pronounced as KAAN BAAN) is a process to maintain inventory
If I m working in a night shift and some inventory is out of stock I will write it down on the card and in morning when other person take over he will first read the card and than fill the inventory.