SDS-PAGE (Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis) is a technique used to separate proteins based on their molecular weight. SDS, a detergent, denatures proteins and gives them a negative charge, allowing them to migrate through a polyacrylamide gel when an electric field is applied. The separated proteins can then be visualized, typically using staining methods, for analysis of protein size and purity.