cross joint, cross member, or flange, you can inspect it by checking it manually, turn it back and forth and inspect if there are noticeable play, inspect it underneath and not by just turning the wheel, turn the propeller itself instead...you can see if the joints are loose then it needs replacement,

you can replace the cross joint only or replace the whole flange, either way you will need that be done on a machine shop

its normal that rearwheels will have play but not too much or it will cause noise during shifting or you can hear it when you step on the accelerator..