refers to the principle that no user should be given enough privileges to misuse the system on their own. For example, the person authorizing a paycheck should not also be the one who can prepare them. Separation of duties can be enforced either statically (by defining conflicting roles, i.e., roles which cannot be executed by the same user) or dynamically (by enforcing the control at access time). An example of dynamic separation of duty is the two-person rule. The first user to execute a two-person operation can be any authorized user, whereas the second user can be any authorized user different from the first [R.S. Sandhu., and P Samarati, “Access Control: Principles and Practice,” IEEE Communications Magazine 32(9), September 1994, pp. 40-48.]. There are various types of SOD, an important one is history-based SOD that regulate for example, the same subject (role) cannot access the same object for variable number of times.
Source(s):
NIST SP 800-192

  A security principle that divides critical functions among different staff members in an attempt to ensure that no one individual has enough information or access privilege to perpetrate damaging fraud.
Source(s):
NIST SP 800-57 Part 2 [Superseded] under Separation of duties