First fix & second fix
First fix and second fix are terms used in the UK construction industry.
First fix comprises all the work needed to take a building from foundation to putting plaster on the internal walls. This includes constructing walls, floors and ceilings, and inserting cables for electrical supply and pipes for water supply.
Second fix comprises all the work after the plastering to a finished house. Electrical fixtures are connected to the cables, sinks and baths connected to the pipes, and doors fitted into doorframes. Second fix work requires a neater finish than first fix.
The division of work is a convenient description because electricians, plumbers and carpenters will probably have to make two separate visits to one property under construction, at separate times. Project managers can report "first fix complete" or "second fix 50% done" and others can understand.
Some construction companies specialise in first fix work or second fix work, but most do both.