To participate in governance, Curve Finance users need to lock their CRV into a voting escrow.
veCRV stands for voting escrow CRV. They are your CRV locked for voting. The longer you lock your CRV for, the more voting power you have (and the bigger boost you can reach). You can vote lock 1,000 CRV for a year to have a 250 veCRV weight.
You can only vote using your voting weight at the block where a proposal was created.