Two-dimensional gel electrophoresis is a laboratory technique used to separate proteins based on their size and charge. In the first dimension, proteins are separated by isoelectric focusing, where they migrate in a pH gradient until they reach their isoelectric point. In the second dimension, the proteins are separated by size using standard gel electrophoresis. This method allows for the analysis of complex protein mixtures, making it valuable in fields like proteomics and biomedical research. By visualizing the separated proteins on a gel, researchers can identify and quantify specific proteins, aiding in the study of diseases and biological processes.