The CELL CHANGE ORDER FROM UTRAN is used to change from a UTRAN cell to a cell in another RAT. It is a little like a handover, but it is intended for non-real-time services, and so is analogous to a forced cell reselection. It is applicable to the CELL_FACH state and the CELL_DCH state (PS connections only), and is used to allow UTRAN to force UEs not using the CS domain to use other RAT cells.
In the reverse direction, it is possible that the other RAT may also cause a CELL CHANGE ORDER TO UTRAN. In this case the other RAT, through some means, encourages the UE to change to a UTRAN cell using information that is provided on that cell. When camped on the UTRAN cell, the UE performs an RRC connection establishment procedure with the establishment cause defined as 'Inter-RAT Cell Change Order'.