Equal opportunity in employment is the idea that all people should be treated equally in the employment process. They should not be discriminated against on the basis of anything that is not relevant to the work that is expected of a person in their job.
In the past, there was a great deal of discrimination in employment. Firms would refuse to hire non-white people for certain jobs. They would refuse to hire women for certain jobs and/or they would pay them less for the jobs they did have. Beginning in the 1960s in particular, the Civil Rights Movement pushed back against this and other kinds of discrimination. Today, discrimination is illegal and firms are required to provide equal opportunities in employment.
Equal opportunities in employment covers issues such as hiring, promotion, and pay. Firms must give all people an equal chance to get hired or promoted. They cannot pay people different salaries unless those people provide different levels of production for the firm.
The idea of equal opportunity forbids discrimination on the basis of factors that are not related to work. A firm may, of course, refuse to hire someone who is not qualified for a job. They may pay a person less than another if that person does not work as well. However, they cannot refuse to hire a person on the basis of such things as sex, race, or religion.
Thus, equal opportunity in employment requires that firms should make their hiring, promotion, and pay decisions on the basis of the employees’ qualifications, not on the basis of things like their race.