Inhibition: The activity of any enzyme is sensitive in the presence of specific chemicals which bind to the enzyme. When after binding of a chemical with an enzyme, its activity stops, then this process is called inhibition and that chemical is called inhibitory.
Competitive Inhibition: When the inhibitor is very similar to the substrate in its molecular structure and inhibits the activity of the enzyme, then it is called competitive inhibition.
Due to the close structural similarity of the inhibitor to the substrate, it competes with the substrate by binding to the substrate binding site of the enzyme. As a result, the substrate is unable to bind to the substrate binding site, resulting in slowing down of enzyme activity. For example, the inhibition of succinic dehydrogenase by malonate, which is closely similar in structure to the substrate succinate. Such competitive inhibitors are often used to control bacterial pathogens.