Etsy defines it as - curated galleries handpicked by the Etsy community
So for those of who who don't know what a Treasury is lets start with the basics.
Etsy started as a handmade community for artisans to sell their creations. The Site has since expanded to include Vintage goods (at least 20yrs old) and supplies. It is the largest site of it's kind with sellers from all over the world.
So many sellers and so little prime exposure. On Etsy the front page is a goal for many sellers getting on the front page insures lots of views. Being in a Storque article, featured seller, Gift Guides and the Main Gallery all get you views, and hopefully sales.
The Main Gallery on the front page is 12 items picked by Etsy to showcase their sellers. It's hard to miss and instantly drives traffic to a etsy shop. If you look in the forums of etsy, you will see tons of threads about the Front Page (FP). How do I get on the FP? Why is it all the same Sellers on the FP? Rants about the Front page. Currently there are 4,561 threads dedicated to the Front Page.
One way to get there? Treasuries. Picked by Sellers. If you are lucky enough to get a treasury slot. You can pick one of your own items and 11 others plus 4 alternates. 16 items in total. 12 For the treasury page and if something sells the alternates get put in the empty spot.
Treasuries are other sellers saying "I like this item" or "this is front page worthy" at it's best. It is being honored by other sellers. Great treasuries (chosen by Etsy staff) are featured on the front page. Of course even the best treasury doesn't always make it. What is the saying? it was an honor just being nominated.
It isn't easy getting a treasury spot. People set up and wait for it. With just 333 spots they fill up quickly. So Etsians wait for one to open up. Craftpolis created a clock, two just to figure out when there will be an open spot. It doesn't always help. If you get a treasury it lasts for only 2 days.
With competition steep to get a treasury and steeper to get to the front page gallery being chosen for a treasury is a good thing. Something to tweet, blog, and basically share. It says somebody liked my item enough to promote it.