The role of class in the Russian Revolution and its aftermath is an endlessly fascinating topic but I'm going to give you the short version here, what with it being Christmas Day and all.

As good Marxists, the Bolsheviks understood class as being fundamentally about an individual's relation to the means of production. Indicators used by other sociologists (etc income, status, etc) were of little use. Someone who owned a factory, and lived off the profits of its outputs, was a capitalist; someone who worked for wages was a worker. Someone who worked the fields was a peasant, a supposedly obsolete class typically considered petite-bourgeoisie. I'm racing through this because the reality was far more complex.

Whereas Marx saw society splitting into "two great hostile camps", with the petite-bourgeoisie uncomfortably squeezed between them, the Tsarist state was less forward looking. Officially a working class did not exist in Imperial Russia - the Tsarist estate system did not allow for the emergence of new social groups. Workers of all stripes, plus many professionals, were still considered by the state to be 'peasants'.

This context is important because much of the work on the class structure of the pre-revolution society (and informing policy post-1917) is based on reconstructions by Soviet historians. Which is fine, we just have to be aware that these were complex identities that don't necessarily sit in the neat little class boxes that they've subsequently been assigned.

With that said, the Russian working class was typically taken to include factory workers, transport workers, municipal workers, artisans and servants. Basically those employed in manual labour in an industrial setting. As per Marx, Soviet historians tended to include white-collar employees (sluzhashchie) in this category, given that they also drew a wage. In reality, however, there were clear differences between these technical or white-collar staff and the shop floor workers; both tending to form their own unions and other representative bodies.

But the elephant in the room in the peasantry. Marx didn't have much time for this class but it was unavoidable in Russia. Ignore for now Lenin's theories on intra-village class tensions, the problem was that there was significant cross-over between the urban and rural worlds. The Russian urban working class was a relatively recent construction, largely created by migration from villages (in 1905 less than 50% of St Petersburg workers were born to working class parents). Throw in widespread seasonal migration for work (otkhodniki) and lingering ties to home villages (both family and land) and the line between worker and peasant becomes quite blurred. Russian workers were considered to have 'one foot in the village'.

Soviet historians and sociologists spent quite a lot of time trying to tease out the differences between new arrivals into industry (assumed to be carrying their peasant prejudices and characteristics) and the more 'proletarian' elements. The rule of thumb they developed was that it took five years of service at the bench to turn a peasant into a proper proletarian, which would mean that 40-50% of Petrograd workers in 1917 were experienced 'cadre' workers.

But treat all such figures and neat definitions with extreme caution. These are abstract categorisations and calculations that can never really capture the complexity and shifting nature of class identity, particularly in a time of revolution. Many of the recent migrant workers were amongst the most militant in 1917. Actual workers could either hold a narrow shop identity (including gender and skill divisions) or subscribe to a broad view of the 'toiling classes' (the demokratiia) that included peasants. What was important in 1917 is that however the workers viewed themselves, with the possible exception of the sluzhashchie, they did so in opposition to the propertied classes (tsenzovoe obshchestvo).

Ultimately, as today, these terms are real but hard to express 'concrete terms'.

Sources

SA Smith's Red Petrograd is probably the best single study of the Russian working class in 1917. Shelia Fitzpatrick has been a leading light on the framework of class in the early Soviet Union; I'd recommend her Russian Revolution as a concise introduction to the period and many of her themes.