Blue-collar workers work most often in a non-office setting (i.e. construction site, production line, driving, etc.) and use their hands and physical abilities to perform their duties.
The name comes from the early 20th century when these workers wore resistant fabrics of darker colors (i.e. blue denim or blue uniforms). They preferred these clothes because they usually got them dirty at work and often could not afford to wash them frequently because of low wages.
Examples of blue-collar employees include construction worker, machine operator, millwright, assembler, and truck driver. The blue-collar job definition does not specify the skill level or type of pay workers receive, they can be skilled, unskilled, waged, or salaried.