Span of control refers to:

AAn orderly line of authority that exists within the ranks of the incident management organization.
BThe act of directing, ordering, or controlling by virtue of explicit statutory, regulatory, or delegated authority.
CThe process of moving the responsibility for incident command from one Incident Commander to another.
DThe number of individuals or resources that one supervisor can manage effectively during an incident.

Command is:

ABased on the ...

Verified Answer :

Generally speaking, span of control refers to "D. The number of individuals or resources that one supervisor can manage effectively during an incident," although sometimes it simply refers to the number that is supervised, not necessarily in an effective manner.