And what is  Round the wicket? 

  Over the wicket  - Bowling arm closer to the stumps 
  Round the wicket - Bowling arm away from the stumps 
  Both terms apply equally to both left-arm and right-arm
  bowlers.

How to remember which is which?

  Do you have a good mnemonic/analogy?

Ron Knight:
  When the ball is delivered over the wicket the hand delivering the
  ball is much more above (over) the wicket than when delivering from
  the other side, when the hand delivering the ball is more round the
  side.  I offer this not as a mnemonic but as my understanding of the
  actual reason for the terms.

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