A quick dictionary search gave me the same definition for both orchard and grove. I usually know which one to use in a given situation, but I had no idea how to explain the difference to my mother when she casually asked on a walk this morning. Are they interchangable terms or are could they be as different as apples and oranges?
The primary meaning of grove is any kind of small woodland, not necessarily planted by people (although it can be). Orchard definitely means an agricultural, deliberately planted patch of trees.