WHAT IS CONSIGNMENT? 
Whether it's the Dolce & Gabbana jacket you fell for then seldom wore, or the Hepplewhite table that doesn't fit the new dining room, your once-loved treasures can be a true joy to someone else. And just think of all the kids' clothing, gear, and equipment that your kids outgrow! That's what consignment shops do—they connect your underloved items with new owners who will adore them!

How consignment works...
When you agree to consign your items to a shop, you're a consignor. You maintain title to your possessions but give the rights to sell these items to the shop, which is the consignee. 
You receive the agreed-upon monetary return after the goods are sold...if they are sold. 
That's consignment in a nutshell. Specifics of consigning with a shop should be clearly outlined in their consignment agreement, which will spell out the monetary return, length of consignment period, price-reduction policies, and so on. These details might be a factor in which shop you choose.

So what's a RESALE shop?
Technically, all shops which sell consumer goods which have had a previous owner are resale shops. That includes consignment shops, donation-only thrift stores, and shops which buy their merchandise outright.
However, most shoppers call a buy-outright shop a resale shop. These shops can, and most do, buy from the general public: you. 

Read more:

The benefits of consigning

Should I select a consignment, buy-outright, or donations-only shop?

What if I want to start my own shop?