An allosteric inhibitor is a type of molecule that binds to an enzyme at a site other than the active site, which is where the substrate normally attaches. This binding changes the shape of the enzyme, reducing its ability to catalyze a reaction. By altering the enzyme's structure, allosteric inhibitors can effectively decrease the enzyme's activity without directly blocking the active site. These inhibitors play a crucial role in regulating biochemical pathways in living organisms. They can be important in drug design, as targeting allosteric sites can lead to more selective therapies with fewer side effects compared to traditional inhibitors that compete with substrates at the active site.