it’s a handover that is done when a neighbor cell provides better conditions (usually better coverage) than the current cell.
In opposition with “emergency” HO, which occur when the serving cell has very bad raio conditions, so an alternative cell must be found otherwise the call will drop.
In the case of better cell, the call has no risk of dropping, there is no emergency, the HO is not mandatory. It is just that the call will have a better “comfort” in the neighbor cell.
regards
pix