Variation orders or what are commonly called change orders. They bid a job knowing the individual responsible for negotiating a contract has no real experience in that line of work being performed and/or that they typically don't do research into it enough to have the issues adjusted prior to contracting them. Any work that deviates from the contract is considered a variation or change and will cost additional to perform. A lot of construction companies and sub contractors do this. For example, you plan to have a new construction and don't specify where you want each outlet. Then you walk the site now that it's framed, prior to drywall going in and decide that you want an outlet somewhere more convenient for something. Now the electrician will perform that work and charge you for the change or variation making additional money. Your plans state the water tap should be at a certain location but you want it 3' to the left? Change order. Its how a lot of subs and contractors make a lot of money on jobs they originally bid out their competition for. It happens on the smallest jobs but it's far easier to get away with when it's a major project and it's being done for the retards that run the Government.