Every smart contract has to run somewhere. That "somewhere" is a blockchain virtual machine (VM) — the sandboxed program that every node on the network executes identically, so that the same input always produces the same output no matter who runs it. The VM you build on shapes almost everything about a chain: which languages you can write in, whether transactions can run at the same time or only one after another, and how much of the existing developer ecosystem you can plug into on day one.
This is a companion discussion topic for the original entry at https://namefi.io/r/en/blog/blockchain-virtual-machines