Cell is the part of Chain Network that has its own subchains, whitelists (GDB) and usualy consists from nodes from the one network region (but not nessesary).
In the code, cell is just an ID that is declared by the cell declaration. This ID is contained in the datum and related with the nodes and chain which should be segmented into parts.
Important: if the node configured as non-celled, it presents for all cells of the network.