See also the entry on: Multitudes
"Multitude is not a poetic notion, but the simple name of the productive singularities whose productivity cannot be reduced to actual production. Paraphrasing Marx, we might call it ‘living labour’. As a power, which is not reducible to any specific act, to any specific mode of existence or to any historical time, living labour is multitude’s mode of being. It is activity that does not materialize into machinery or products but rather retreats from materiality and turning into actual products. This is precisely how we might describe the transformation of economy: from the confined or restricted economy where it was necessary to distinguish between work and leisure, production and reproduction, life and politics to general economy; where factory-office and its borders have dissolved into society; where the “foundation of productivity is no longer in the capitalistic investment but in the investment of the social brains... where the maximal amount of freedom and the breaking of the disciplinary relations becomes the absolute foundation of creating wealth” (Negri, 1998: 139-140). Thus, to ask ‘what is multitude?’ means not to affirm ‘the end of work’ nor, on the contrary, to announce that ‘everything has become work’, but rather to change the principles of assessment, to change the way of conceiving the ‘the value of value’. This revaluation is not a solution to a problem but rather an opening of potential: it reveals the nature of multitude as a question. Without this questioning multitude will remain abstract, deprived of meaning."
The follow-up of Michael Hardt and Toni Negri's classic book on globalization and the multitudes, Empire.
Here's a review of the book Multitude by Pierre Macherey, in French: