Lightning Pool is a peer-to-peer marketplace for Lightning node operators to buy and sell channels.  Sourcing inbound liquidity can be an issue for Lightning node operators. This can lead to a liquidity crunch. Without enough liquidity, buying and selling through the Lightning network is much more perilous. That’s where the Lightning Pool comes in.

Taking a step back, consider that the Lightning Network was designed to reduce congestion on the bitcoin blockchain. It’s a second layer tech, providing an off-chain transaction network while allowing holders to retain custody of their BTC. One of the issues that node operators often find is the lack of inbound liquidity which limits your ability to receive payments. Previously node operators had just a few ways of sourcing inbound liquidity - Thor for example - and those with lots of liquidity had no easy way to lease that liquidity.

It works like this: Node operators can submit a request on Pool to lease their existing outbound liquidity to a node that requires liquidity. Other nodes can submit a bid to lease these channels for extra liquidity. Like water seeking level, this benefits participants on all sides, while maintaining the core features of decentralized finance overall. Thus, sellers on the pool can earn BTC without giving up custody or involving a third party like an exchange. Yields are earned from buyers on the pool who pay a premium for access to new capital on the Lightning Network without counterparty risk.

Keep in mind that on the Lightning Network the total amount that will be transacted is controlled by the amount that is dedicated to that channel - liquidity.  The Pool helps with this by directly connecting capital with operators.

In essence, the Pool creates a channel lease marketplace and a conventional style auction for buying. This channel lease marketplace (CLM) allows users to trade incoming channels, using a Lightning Channel Lease (LCL). This lease provides the pathway, connecting capital to the places it is needed most. There’s even a built in scoring system for nodes, although pool participants can opt out of it.

Decentralized finance, aka LiFi, by comparison to traditional finance, is still very young.  With the Lightning Network, there are rewards for those who stake capital in the system. Those incentives are shared by participants on the network, so those contributing capital are rewarded with a passive investment.  To try out lightning pools, at present, you'll need to be running lnd version 0.11.1-beta or higher and download poold.

For further details please read this detailed explanation.