In constitutional law, there are a lot of isms.
Textualism claims that the Constitution’s text is binding. The central idea is that judges are bound by the written words of the founding document. (Reasonable textualists acknowledge that the text is often ambiguous. What, for example, is meant by “the freedom of speech”? That is far from obvious.)
Originalism, which is on the ascendancy on the current Supreme Court, insists that the Constitution should be interpreted in accordance with its original public meaning — its meaning at the time of its ratification in the late eighteenth century, and after the Civil War for the Thirteenth, Fourteenth, and Fifteenth Amendments. (Reasonable originalists acknowledge that the original public meaning is often ambiguous. What was the original understanding of the constitutional provision granting “executive power” to the president? That is not obvious.)
Living constitutionalism claims that the meaning of the Constitution evolves over time, which means that the document might require states to recognize same-sex marriage now, even if it did not require that before. (Reasonable living constitutionalists acknowledge that judges can go in terrible directions. From American history, you can take your pick.)