Police forces across the country will change the way that they deal with missing people following failures in cases such as the Rochdale child sex ring.
Plans announced will stop officers getting called out to around a third of missing people cases.
The aim is to free up officers' time and to improve the way forces deal with children who repeatedly go missing from care, and might fall prey to sexual abuse.
Pilots of the new system have been carried out in Greater Manchester, West Midlands and Staffordshire, and Sussex Police has been using the definitions for three years.
Figures from the pilot showed that under the new system around a third of missing people cases are likely to be classed as "absent", and therefore officers will not attend. In one force 31% of cases were classified as absent, and in another 39%.
Chief Constable Pat Geenty, the lead for missing people for the Association of Chief Police Officers (ACPO), said: "Whenever we get a call and someone is reported missing, we would normally dispatch a police officer, irrespective of the circumstances of the case. So you see that's a huge demand on police resources."
Police deal with around 327,000 reports of missing people per year, the equivalent of around 900 per day, two thirds of which involve children.
Under the plans, call handlers will class missing persons cases as either "absent", when a person simply does not arrive where they are expected to be, or "missing", where there is a specific reason for concern.
This can be that the disappearance is out of character or that they may be at risk of harm.
Mr Geenty said police are sometimes used as a "collection service" for children who go missing from care homes.
He said: "What we're asking for now is that the care homes act as responsible parents, do the initial work that's required in terms of trying to find out where the missing individual is, and then if they have concerns to ring the police.
"There is an element about reducing bureaucracy, but I am convinced that the change will enable us to focus resources to protect those children that we need to protect."
Under the plans, each force in the UK will have missing persons co-ordinators who will check whether a child is going missing frequently to detect any patterns of behaviour.
Peter Davies, ACPO lead for child protection, said: "In a number of cases there is a link between children going missing, often repeatedly, sometimes more than once a day, and being subjected to sexual exploitation and other forms of harm.
"What that tells us is that the previous approach to this left something out. There's a very simple message here which is that we are learning lessons from the last two years and we're trying to improve the performance in identifying, understanding and managing the risks to vulnerable children and young people."
However David Tucker, head of policy at the NSPCC, said the charity fears the new definitions could put children at risk.
"We are very concerned that the new definition of 'missing persons' will put vulnerable children at risk of being groomed and sexually exploited," he said.
"The length of time a child goes missing is irrelevant because they can fall into the clutches of abusers very quickly.
"Children go missing for a variety of reasons; they may be bullied, abused or are generally unhappy. But whatever the reason, this problem must be taken seriously.
"We expect all professionals including the police to invest the right amount of time and take the necessary action to protect all children as soon as they go missing."
In the Rochdale case, nine men were jailed in May last year for grooming and abusing vulnerable teenage girls.
A report by the Rochdale Borough Safeguarding Children Board painted a picture of girls as young as 10 being targeted for sexual abuse having been written off by those in authority who said they believed the children were "making their own choices" and "engaging in consensual sexual activity".
Twelve council workers came under investigation for failures in relation to the case, and both the police and Crown Prosecution Service were forced to apologise for missing a chance to stop the gang in 2008.
Solicitor Alan Collins from law firm Pannone, which represents two of the victims, said of the changes: "What is needed is the recognition that when a teenager goes missing it is a serious matter that should be treated as a potentially serious crime, rather than as we have seen happen, being dismissed as some kind of 'life style choice'.
"Going missing is often a symptom of something seriously amiss in the child's life and as we know all too well, often linked to abuse."
Missing People chief executive Jo Youle said: "Regardless of whether the police classify a child or young person as missing or as absent, it must be recognised that there is always a wider safeguarding issue.
"Current evidence suggests that it is important for police to ensure that a missing persons co-ordinator is in place to monitor patterns and identify risk, that return home interviews are provided for missing and absent children and young people, and that police work closely with statutory and voluntary sector partners across the different categories."