What is “blockchain” in simple terms?

[uptrendfinancialsignal]

I was just checking one crypto app this morning and I don't understand a thing. People say “blockchain this blockchain that” everywhere. I thought it was just a normal database, until I saw one breakdown and still didn’t fully get it. Everybody is trying to become a blockchain expert online, but deep down I feel most people are just craming the whole thing. What exactly is Blockchain?