What it is
Constructed for real
Build is where the product is actually made. Work happens in earnest, generating evidence and passing reviews as it goes, but stays isolated from production traffic and customers.
Why separate from launch
Two different risks
Building and shipping carry different risks. Keeping them apart lets the messy, iterative part move fast with no chance of a half-built feature reaching a real user.
A worked example
Done is not live
A feature can be complete and reviewed in Build and still not be live. Going live is its own gated step — never a side effect of merely finishing.