Initial Block Download
The one-time process of downloading and verifying the entire chain when a node first starts.
Initial block download, often shortened to IBD, is the process a fresh node goes through to fetch and re-verify the complete history of the blockchain before it is useful. It is the slowest part of running a node and can take from hours to days depending mainly on disk speed and internet bandwidth. The node validates every historical block, not just downloads them, which is why a solid-state drive matters so much. Progress is best tracked by comparing the node block height against the current network tip. An interrupted initial block download resumes from the last verified block rather than starting over, so the node never loses confirmed progress to a simple restart.