A substantive due process is the fundamental constitutional legal theory upon which the Griswold/Roe/Casey privacy right is based. The doctrine of Substantive Due Process holds that the due process clause not only requires "due process," but also protects basic substantive rights.
Substantive rights are those general rights that reserve to the individual the power to possess or to do certain things, despite the government’s desire to do the contrary. Examples of these rights are freedom of speech and religion. Procedural rights are special rights which dictate how the government can lawfully take away a person’s freedom or property or life, when the law otherwise gives them the power to do so.
The due process clause of the Fourteenth Amendment, which was adopted in 1868, states "nor shall any State deprive any person of life, liberty, or property, without due process of law . . . " It is clearly stated in this passage that a state has to use sufficiently fair and just legal procedures whenever it is going to lawfully take away a person’s life, freedom or possessions. Therefore, before any person can be executed, imprisoned or fined for a crime, he or she must get a fair trial, based on legitimate evidence, with a jury, etc. and these are what you call procedural or process rights.
However, under substantive due process, the Supreme Court has developed a broader interpretation of the clause, one that protects both basic substantive rights and the right to process. Substantive due process holds that the due process clauses of the Fifth and Fourteenth Amendments guarantee not only that appropriate and just procedures be used whenever the government is punishing a person or taking away a person’s life, freedom or property, but that these clauses also guarantee that a person’s life, freedom and property cannot be taken without appropriate governmental justification.