When i started this blog i didn't realize that the term op-shop isn't universal. Oops. So i will do my best to come up with a definition.
Op-shopping is when you purchase items from charity stores, its very similar to thrift shopping which is what they call it in america i think? The 'Op' part of the word is short for opportunity, i guess this is because its a great opportunity to find some really nice items/garments. Also because op-shopping is buying from charity shops it gives the less fortunate an opportunity to better themselves through the work of charities such as Salvation army because in a round about way your donating?
Any way hope this helps, if this makes no sense what so ever, which is highly likely (I'm not the best at explaining) you could try Google it.