Alright, let's dive into this.

So, with traditional Bitcoin transactions, each one has a unique transaction ID (txid). This is because each transaction is recorded on the blockchain for everyone to see.

But with Lightning Network transactions - also called "off-chain" transactions - they don't get their own txids. This is because they're not individually recorded on the blockchain. Instead, only the final state of a series of transactions between two parties gets recorded when the channel closes.

Think about it like keeping a tab open at your local pub. You and your mates might order dozens of rounds throughout the night, but all those orders aren't individually reported to your bank as separate charges. Only when you close out and settle up does that final amount hit your account.

As for "second layer," it means that Lightning Network runs "on top" of Bitcoin but isn’t part of Bitcoin's core protocol itself – kind of like how email runs on top of Internet Protocol (IP) but isn’t part and parcel with IP itself.