For most people in the world, being rich or poor doesn't mean whether or not you own a fancy car, can dine out or go on holidays.
It's much more fundamental than that. It's whether you can afford to live in a permanent structure rather than a tent, whether you can afford to include meat in your diet more than once a week, or if you can afford to buy medicine to treat your sick child.
And deciding who's poor and who isn't can be crucial in determining how global financial resources from aid agencies and governments are deployed.
But exactly how to measure poverty is something that's occupied the minds of many researchers over the years. Just this month, boffins at the United Nations University – the UN's research arm – have again pondered the topic.
They point out that currently used standard measures of poverty are merely snapshots based on current income and don't take into account a person's history of poverty.
"Without taking into account a person's history of 'poverty spells' – the timing, length and severity of previous poverty episodes," argue UN researchers Luc Christiaensen and Lorraine Telfer-Taivainen, "it remains hard to know how poor that person really is."
They say that people with long poverty spells in the past are less likely to escape from poverty.
"And if they do, they are far more vulnerable to becoming poor again," they say.
"The timing of the spell also matters, with childhood poverty being especially detrimental. It can hurt children's cognitive development, their prospects of marriage and lifetime earnings."
It sounds rather depressing and easy to wonder whether people in poor nations have any long-term hope of seeing a better future.
But it would be wrong to despair completely.
The World Bank reckons that in 2008, 22pc of the world's population was living on less than $1.25 a day. That's an awful lot of people, but better than the 52pc that were in the category back in 1981.
And even though the world's population has grown significantly from 4.5 billion in 1981 to 6.7 billion in 2008, it still means that 1.3 billion people were surviving on $1.25 a day in 2008 compared to 2.34 billion back in 1981.
And between countries, the manner in which poverty is calculated obviously varied. Take even so-called food poverty.
A study last year for the Department of Social Protection considered that very subject.
It said that just over 14pc of the population reported food deprivation under the category of not being able to afford having friends or family over for a drink or meal. More importantly, just close to 3pc of people said they couldn't afford a meal with meat.
By so many measures, Ireland is and remains a rich country.
Its per capita GDP remains one of the highest in the world despite the financial crisis, and it has social, political, economic and physical infrastructure that many other nations can barely dream of.
But undoubtedly, there is severe and genuine hardship all over the country. It's just that the definition of poverty is radically different around the world.
Determining how to define poverty is important from a domestic point of view too, because it enables governments to establish the types of social safety nets required to prevent citizens falling below the poverty line, and also help them to escape poverty.
"Countries can use studies on poverty spells, for example, in their analysis of the middle class (which some define as people who aren't at risk of falling into poverty for a specific period of time)," according to the UN researchers.
"And if the length of poverty spells affects a person's ability to escape from poverty, a person's poverty history needs to be considered when deciding about the graduation from safety net benefits."