Refurbished, reconditioned, pre-owned, certified pre-owned... it's all a bit confusing really.
In this industry 'refurbished' is a general catch-all for pre-owned or secondhand devices. Even though refurbishment implies taking a device and fixing faults or imperfections, it's often used to describe any fully functional secondhand phone. This is more to do with the widespread use of the term than any intention to mislead.
Before the secondhand market had matured with the introduction of consumer trade-in programs, the major supply of used phones was via customer warranty returns. By the nature of these returns, most were faulty and required repair to make them good again. And economically it makes sense to either repair the device, or use parts from the device to repair another. Which is great if done well.
Unfortunately this repair process hasn't always lead to great results. Whether due to the immature nature of the category, the complex nature of the repairs, the drive to keep costs low, lack of understanding or intentional neglect, in the early days we saw a lot of product sold as refurbished coming to market at a good price point but either lacking good reliability, or downright faulty from the outset.
Thankfully those days are mostly past. Markets evolve, and those able and wanting to improve survive, while those not up to the chase get left by the wayside.
In the meantime we've also seen huge growth in consumer opportunities to generate cash for their perfectly good unwanted tech. What started as person-to-person transactions on auction sites has quickly grown to be driven by corporate trade-in programs run by the big network providers and specialist companies such as Gazelle in the US. Where previously only faulty product was available on a commercial scale, now we have 100% functional product, distinguishable from new only by their cosmetics (the way they look/signs of wear) and maybe the odd tired battery. And with the advent of solid state/flash hard drives, fewer moving parts means increased longevity. Which is all good news for product which may only have become redundant due to fashion or its owner's desire to have the latest thing out.
So now we have a variety of secondhand product available to purchase. Refurbishment, the first kid on the scene, Pre-owned, the fancy name for secondhand (but nothing necessarily wrong with it), and a bunch of other technically different terms such as Reconditioned (a soft form of refurbishment, maybe just a battery replaced) or Certified Pre-Owned (CPO); manufacturers' such as Apple or other third-parties' stamp for the process of testing, verifying and certifying the 100% functionality of a secondhand product.
While it remains a little confusing, the good news is these days all these terms tend towards the same thing: a good quality product, not much different from new, backed up by solid warranties, which will do the job at hand for a great price and, to top it off, means one less brand new device unnecessarily brought into the world. What's not to like about that?