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. When more substrate is available, it is more likely to bind to the enzyme than the competitive inhibitor. This relationship is important in understanding enzyme kinetics and is relevant in fields like pharmacology, where drugs may act as competitive inhibitors to regulate biological processes.