This term refers to the compression that a group (chemical entity) suffers by being too close to its nonbonded neighbors. If an enzyme and a substrate try to come together in order to react, but the substrate has on it a bulky group that disallows close contact between the two (because the group bumps into the enzyme), then the reaction will not occur because of steric hindrance. Seen in another way, two chemical groups bump into each other and cannot get by each other because they are held in place by the bonds binding them to other atoms. Hindrance of movement or activity occurs because chemical groups bump into each other and cannot occupy the same space.