WHICH TYPE OF CONSIGNMENT OR RESALE OR THRIFT SHOP SHOULD I CHOOSE?
All shops that sell gently-used goods are resale shops. Within resale, there are consignment shops, buy-outright shops, and thrift shops.
Consignment shops accept merchandise on a consignment basis, paying owners a percentage when and if the items are sold. Most pay consignors from 40% to 60% of the selling price, and have a policy of displaying goods for anywhere from 60 to 90 days. Usually unsold items can be redeemed or the shop can arrange for them to be donated to worthwhile local charities.
Buy-outright shops purchase items they can resell from individuals or wholesale sources. 
Thrift shops raise money for nonprofit charities. These range from The Salvation Army and Goodwill types to the smaller church-based shops run by volunteers. They obtain goods through donation or consignment. Some thrifts do both.

BUT IT MIGHT BE CALLED SOMETHING ELSE IN YOUR NEIGHBORHOOD!
Depending on where you live, and where you're from, and where your neighbors are from, local usage of these terms may vary. It's easy enough, though, to figure out which type of shop is which: just ask! Any shopkeeper is more than happy to explain her (or his) business to you!

WHICH IS BEST FOR ME?
If you enjoy sharing in the profits, and the risks, of consigning, become a partner in the process with a consignment shop. To clear out items you wish to pass on with little fuss, a buy-outright shop's procedures might suit you better. And finally, for clean, usable (but not necessarily terribly fashionable) possessions, donate to a thrift shop whose charitable mission resonates with you.