Blockchain is the name for an encrypted, digital peer-to-peer network. It utilizes a long, distributed list of all the addresses that money is distributed to. A more accurate, but easy to understand description can be seen here:
https://www.youtube.com/watch?v=SSo_EIwHSd4
A blockchain has more applications than just digital money, but Monero's goal is singular: it is a digital currency that is decentralized. Meaning that no central agencies, companies or institutions have control over the flow of money. And in contrast to most other decentralized digital currencies, Monero is 100% private and fungible. More information on these technologies can be read about in the book Mastering Monero:
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A side effect is that this limits the frequency of transactions that can be sent in quick succession. This might result in a UX problem for people that need to send multiple times in quick succession.
Monero's Block Time is 1 minute. But it's recommended for wallets to wait for a certain amount of confirmations before allowing new transactions. This results in a locked part and an unlocked part of your balance.