Handover 
Redirection Cell Selection Cell Re-Selection.
HO:
When the user moves out of coverage of one cell to another cell. For smooth operation and to avoid call drop.
HO happens only in case of connected user.
Redirection:
When UE changes its RAT, cell redirection happens. and in redirection UE goes from connected state to idle state.
and when a particular service and coverage is not available to one cell, the UE is redirected by the eNB to other cells for better coverage and respective service requested.
βοΈ Cell Selection:
In Idle mode, when UE is not RRC connected to any particular cell, but it camps on a cell instead.
In idle mode, the procedure of camping on a cell is called cell selection.
Cell Re-selection:
When UE moves out of coverage of one cell to another cell in idle mode, UE has to camp from one camp to another cell.
This process of reselecting a new cell, while UE is already camping on an existing selected cell is called Cell Re-Selection.
Credits: 