What Is a Cryptocurrency
Sending is instant. Being confirmed is a different state.
A transaction is the entry, a block is the page, the chain is the book. Until your entry is on a page, the network knows about it — and nothing more.
The problem
You pressed send. Now watch it get buried.
Sign the payment, then let blocks be found one at a time. Read the cost line after every one.
One payment, from pool to depth
NOT SENTNothing has been sent yet. Press Sign & send it.
Sent and confirmed are two different states. Between them the transaction is real, signed and checked — and still sitting outside the chain, where it can simply be left out. Only inclusion in a block anchors it in the transaction history. From that point on, confirmation is not a switch that flips: it is depth.
Notice what the cost line never said: impossible. Nothing in the design forbids a rewrite. What stands in the way is the work — an attacker would have to redo every block from yours upward and then outrun the honest network, which is adding blocks the whole time. That is what people mean by immutable: not a magic lock, but a bill that grows with every block and is already too large to be worth paying.
The definition
Three things people get wrong about confirmation.
Tap each card for what is actually happening.
Hands on
Who picks, and who checks?
Miners and nodes are not the same participants doing the same job. Switch sides.
Miners
SELECT & PACKAGESelection, checking and acceptance interlock — the power does not sit with the miners alone.
The bridge
Entry, page, book — and why order is the point.
The whole path in five moves, from a signature to a place in the sequence.
Transactions are the content, blocks are the ordered packaging. What this lesson took for granted is the block itself simply appearing — who produces it, why that costs anything, and why a rewrite has a price at all. That is mining, and it is the next lesson.
Check yourself
Five questions.
Answers come straight from this lesson. Submitting completes it.