Total amount of value extracted from labor power. The increase in surplus value in absolute terms occurs through a reduction in the hourly wage or an unpaid increase in working time.
Definition in "Capital"
The surplus-value produced by prolongation of the working day, I call absolute surplus-value. On the other hand, the surplus-value arising from the curtailment of the necessary labour-time, and from the corresponding alteration in the respective lengths of the two components of the working day, I call relative surplus-value.
Karl Marx. Capital, Book I, Chapter X, 1867.
Absolute surplus value in the class struggle
For capital, increasing absolute surplus value simply means paying less per hour worked: lowering wages, signing 4-hour contracts that then turn out to be full-time, working unpaid overtime, etc.
The less capitalized a sector or a region is, the more urgent, in the face of crisis, is the need to increase exploitation in absolute terms. That is why the tendencies towards pauperization appear first in the countries with the weakest national capitals and, within each country, in the sectors with the greatest difficulties of capitalization.