The more common term is "fraudulent asylum seeker". It's defined as anyone that fabricates something about their background in order to qualify for refugee status. This could be any number of things, but the most common are:
* lying about persecution. For instance saying the government wants to kill you, when in reality there is no such threat.
* lying about country of origin. Like saying one is fleeing Syria when in reality they are economic migrants from peaceful countries. https://foreignpolicy.com/2015/10/07/the-men-who-pretend-to-...
* lying about age. Some countries have more permissive rules for minors, so adults lie and say they are children. Poland studied this, and found about 40% had lied about their age: https://www.polsatnews.pl/wiadomosc/2019-09-18/niemieccy-eks...
The fact that some governments aren't bothering to try and detect asylum fraud means there's no available data. But that doesn't mean it's not happening. It's like a company that has no sexual harassment reporting mechanism claiming no harassment happens because it has never had any reports of harassment.