What is disparate discrimination?

There are two terms that use the word "disparate."
Disparate TREATMENT means the employer treats people differently for the wrong reason. The employer uses somebody's race, age, sex, religion, etc. to change the terms and conditions of employment.
Disparate IMPACT means that the employer has a rule or policy that at first would seem to be fair and neutral to all people, but in reality it has the consequence or unintended effect of being tougher on people of certain groups.

For example, in the 1970s a power company in the deep South had a requirement that all their employees had to have a high school education and pass a general education test. Most white people passed the tests but a lot of black people failed. Because the public education system was racially unequal in the South in the 1940s and 1950s and 1960s, the power company's rule excluding a lot of black Americans from getting (or keeping) their jobs. That is unlawful under Title VII of the Civil Rights Act of 1964. Even though "well educated" versus "poorly educated" are not suspect classifications when it comes to federal employment law, at that particular time and place in American history any rule against poorly educated workers would be just like having a rule against hiring blacks.