Non-competitive inhibitors are substances that reduce the activity of an enzyme without competing with the substrate for the active site. Instead, they bind to a different part of the enzyme, altering its shape and function. This means that even if the substrate is present, the enzyme's ability to catalyze a reaction is diminished. These inhibitors can affect both the enzyme-substrate complex and the free enzyme, leading to a decrease in the overall reaction rate. Non-competitive inhibition is important in regulating metabolic pathways and can be found in various biological processes, including those involving enzymes and metabolites.