First Fix stage - what does this mean/include?

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I am in the process of negotiating some building work and the builder has agreed to complete 2 rooms (a study and shower room) to first fix stage, but I am unclear as to what this actually means - Does it include hot, cold and waste water feeds as well as electrical wiring to socket/switch boxes, but not actually fitting the sockets/switches etc?

Any clarifications would be greatly appreciated,

Thanks