Liquid is a sidechain operated by a federation of companies in the Bitcoin space. It uses L-BTC, a token pegged to bitcoin, as it's currency. You can use this to see how much bitcoin Liquid has and what the health of the peg is. https://liquid.network/

You get some interesting benefits with using Liquid, mainly being improved privacy, faster settlement, and lower fees (as long as Liquid usage is lower than base chain). IMO the best use case for it today is a place to build enough sats for a swap to the base chain with a single large UTXO (1m sats minimum, ideally more). Your sats are generally safer on Liquid than an exchange, but less safe than base layer, so I think of it as a middle ground.

Given that this is a federation, there are trade offs to be aware of. There is the risk of a rug if the vast majority (I want to say 11/15 but dont quote me on that) want to act maliciously. I believe they can also censor txs. Understand the companies involved in the federation and whether or not you're comfortable with this trust model. Again, not ideal for life savings, but maybe for working capital 🤷‍♂️. https://liquid.net/