The majority of Solend TVL sits in a global main pool and a series of smaller isolated pools and permissionless pools.
Tokens can be listed in the main pool if they do not represent an increase in risk, mainly by having reliable oracles or thick liquidity to assist in liquidations. Most tokens will be listed on Isolated pools first before proceeding to Main pool after sufficient time.
Isolated pools are smaller pools that are used to list slightly riskier tokens such as Locked Staked IN (lsIN) or future tokens like xSTEP or SAMO. As these tokens have less liquidity and are more volatile, they might be an exploitable opportunity or a risk for the main pool, isolated pools are used to screen/quarantine them before adding them to the main pool.
This way, any exploit or risk will only affect the smaller TVLs present in the isolated pools instead of risking the bulk of TVL in the main pool.
Permissionless pools allow anyone to create an isolated pool on Solend. The creator decides and earns 20% of origination fees generated in that pool. Therefore, a successful Permissionless Pool means success for the pool creator.
There will be many more isolated pools to come. If you're interested in a particular one, bring it up on Discord, or come join our #permissionless-pools channel in Discord to talk about new pool ideas!