Let’s go over a few definitions first:
Sell-order: It’s an intent to sell an NFT (or one NFT from a defined set of NFTs) at a certain price that’s posted by the owner of the NFT (seller) on a marketplace. For example, a single listing of a DeGods NFT at 300 SOL is a sell order.
Buy-order: It’s an intent to buy an NFT that meets certain criteria at a certain price, that’s posted by the buyer on a marketplace. These criteria can be so specific that points to a single NFT (aka a single bid or offer on a single NFT), or they can be so general that can be met by any NFT from a collection (aka a collection offer).
Sell-side liquidity (aka liquidity pool or LP): It’s one or more sell orders.
Buy-side liquidity (aka liquidity pool or LP): It’s one or more buy orders.
Double-sided liquidity (aka liquidity pool or LP): It’s one or more buy orders followed by one or more sell orders (imagine all of these orders are sorted by price). In other words, a double-sided LP is a buy-side LP followed by a sell-side LP.