Sure--"non-reference" means a design for the cooling on the card (the fans, mostly) that is something other than what AMD or nvidia suggested on their original model. But usually people just use it as shorthand. Reference coolers tend to exhaust air out the side of the case (axial cooling--along the axis of the card). This keeps the inside of the case cooler, but it's harder to do well, so it results in worse cooling for the actual GPU. Non-reference coolers tend to be open air models, i.e. they exhaust heat into the case, so you need good airflow within the case to make them work. But they give better cooling performance for the graphics card in general.
Basically you can tell if it's non-reference by looking at the card: it will likely have much more surface area devoted to two or more fans, instead of just a single fan and a lot of plastic casing. The non-reference cooler cards tend to be at least $10 more expensive, but sometimes $20-40 more expensive if the card is also overclocked right out of the box.
You can overclock basically any modern video card by using either AMD's own driver suite (Catalyst), which you will have to have as part of the software for the card, or using a specialized utility such as Trixx or Afterburner, which are pieces of software made by Sapphire and MSI. You should really consider overclocking if you're getting a 7850, because it's a great card for it (akin to the 2500k in the processor sphere).