A defects liability period is a stretch of time written into a contract, usually starting at practical completion, during which the client can notify the contractor of defects and the contractor must come back and fix them at its own cost. It is most common on commercial work and on subcontracts under a builder, where the contract sets the length; twelve months is a common figure, but the contract can say anything. It is often tied to retention: the money held back is released, or the last of it is, when the period ends and the listed defects are fixed.
The end of the period is not the end of your responsibility for the work. It ends the contractual process for calling you back. Statutory warranties under state home building laws, the consumer guarantees in the Australian Consumer Law and ordinary claims for defective work can all reach further than it. Treat it as the time when coming back is your job by contract, not the time after which nothing can be asked of you.
In practice
An electrician wires a shop fitout for a builder under a $60,000 subcontract, with 5 per cent retention and a twelve-month defects liability period. The builder holds $3,000 across the progress claims. Half of it, $1,500, is released at practical completion. In month eight, two emergency lights fail their test, the builder notifies the electrician in writing, and the electrician replaces them at no charge within the week. At month twelve, with the defects list cleared, the electrician claims the remaining $1,500.
The money most often lost here is not lost to an argument. It is the second half of the retention that nobody asked for. Note the end date of every defects liability period the day the job reaches practical completion, and send the claim for release when it arrives.
On a homeowner's job there is usually no formal period at all. Customers are more likely to talk about your warranty on workmanship, which is a different promise and one you set yourself.