A SPAN port or Port Mirror differs from RSPAN technology in which way:

A SPAN port captures traffic locally, an RSPAN captures traffic remotely

A SPAN port captures traffic consistently, an RSPAN captures traffic randomly

A SPAN port captures multiple ports while an RSPAN is "relational" and captures multiple VLANs (Relational LANs)

They are both the same with different terms being used by different vendors

A SPAN port is used on a Switch while a RSPAN is used on a Router