Internal mobility is defined at CERN as:
a change of functions: new job in the current organizational unit or in a new one.
a change of organizational unit : change of department, group, section, with or without a change of functions.
an internal detachment: temporary change of functions or of organizational unit.
(see Administrative Circular N°17 (Rev.1))
Internal mobility may be instigated by the Organization or upon proposal of the staff member.