Competitive inhibitors are molecules that resemble the structure of a substrate, the substance an enzyme acts upon. They bind to the active site of an enzyme, preventing the substrate from attaching. This competition for the active site can slow down or halt the enzyme's activity, affecting the overall reaction rate. These inhibitors can be overcome by increasing the concentration of the substrate. As more substrate molecules are available, they can outcompete the inhibitor for the active site. This relationship is crucial in understanding enzyme kinetics and is often studied in the context of biochemistry and pharmacology.