The previous educator gave a great response. I will simply expand on it to provide more context, within his example of racial discrimination.
As he mentioned, from 1896 to 1964, the South practiced Jim Crow, which was legal, or de jure, segregation. De jure, like de facto, is a Latin phrase. In English, it translates to "in law."
Legal segregation, or Jim Crow, existed in the South as a result of the Supreme Court decision Plessy v. Ferguson, which ruled based on the "separate but equal" premise. Of course, segregation enforced inequality, which was decided in 1955 with the Brown v. Board of Education of Topeka, Kansas decision. The 1955 case determined that school segregation was unconstitutional. However, segregation in public accommodations persisted in the South. Blacks and whites used separate restrooms, rode in separate sections on buses and trains, and occupied different sections of theaters. Accommodations for blacks were routinely sub-standard.
Notice, though, that the Supreme Court decision in Brown was in relation to school segregation in Kansas. Kansas was a non-Southern state that practiced segregation in schools. Illinois, particularly Chicago, was also notorious for segregation. Chicago practiced segregation in housing. Redlining, a discriminatory practice in which banks refused to give mortgage loans to blacks for houses in predominately white neighborhoods, was a common practice. Discrimination in housing led, not only to school segregation and a difference in the maintenance of certain neighborhoods as well as allocation of resources, but also allowed for predatory practices in which blacks were given loans at much higher interest rates than white borrowers.
De facto segregation was every bit as detrimental as de jure segregation in the South. However, the former was more insidious, while the latter was overt and strictly enforced.
De jure discrimination is any discrimination or unequal treatment of two differing groups that is based on statutory law and sanctioned by the government in place at the time. The best example of de jure discrimination would be the Jim Crow laws of the segregated south after the Civil War up to the passage of the Civil Rights Act of 1964. These laws put in place two separate but unequal societies in the south, allowing the white power structure to subjugate the black population of the former confederacy. The Apartheid system in South Africa up to 1994 is also an example of de jure discrimination.
De facto discrimination, defined as "in fact" discrimination, is conducted below the surface of legal activity, and is more systematic and institutionalized. It involves preventing one group from receiving equal protection of the law, as required by the 14th Amendment by way of secretive, underhanded, and institutionalized maltreatment of a minority group. Discrimination in housing, jobs, and education that goes undetected in the courts counts as de facto discrimination. Such action is subject to litigation under numerous civil rights laws passed in the 1960s and 1970s.