'Wages' are usually hourly, daily, or weekly, and are frequently associated with manual labor;
'salaries' are often a fixed monthly payment, and are associated with professional or office work.
According to dictionaries, the first known English use of 'salariat' is from 1917.
But its use as a French term predates that, as can be seen in this 1904 book review:
"...he points out there is no necessity for the 'salariat' to be also the 'proletariat'. The existence of a proletariat does not depend on the fact that the services of a large class are renumerated by a time-rate of wages, but on the insufficiency of those wages, the insecurity of the work, and the position of dependence in which the wage-earner is placed in regard to his employer....M. Bourguin is of the opinion that the beneficient action of the employers themselves, the influence of trade unions, and, above all, legislative action, will in the future bring about all these desirable reforms. He admits that this view may be considered optimistic, but explains that a certain amount of optimism is necessary in human affairs as tending to produce the very results desired."
- Christabel Osborn, from a review of Les Systèmes socialistes et l’évolution économique by Prof. Maurice Bourguin