It’s the “floating middle class”. From the Semacraft Blog:

the floating middle class has grown to over 20% of the population. This segment between the poor and the established middle class, is the only part of the economic pyramid that has had significant growth over the last 20 years achieving 100% growth in the last 30 years. They maybe susceptible to shocks that easily push them back into poverty but unlike their counterparts living in abject poverty, they have money to spend. With a population of 1 billion people, approximately 700million of whom have mobile devices,  I can easily suppose a significant number of the floating class are connected

Not everybody agrees with this view, however. When the African Development Bank coined the term last year (pdf), it attracted lots of criticism.

Without knowing, people leading the same miserable lives have suddenly been catapulted in the enviable position of middle class. Nothing has changed except the label.

..The ten poorest countries in the world are in Africa but AfDB with innovative statistic has changed the status of a lot from poor to floating middle class. They are floating on a busted canoe, scooping out the water in order not to sink. The canoe is the asset.

I see the point here: calling “middle class” people earning 2 to 4 dollars a day is a  is bad idea. To me, that seems closer to extreme poverty than to the actual middle class. But at the same time, if a large chunk of the population has really increased its earning capacity, as the AfDB study suggests, this is undoubtedly good news. I think that there’s nothing bad in acknowledging these new realities, however imperfect they are, and seeing them as a new opportunity for promoting markets and further upward mobility among the low-income population.

Some further readings here.