It refers to an enzyme's shape and conformation changing over time in response to substrate binding.
This makes the enzyme catalytic, lowering the activation energy barrier and increasing the reaction's completion rate.
When substrates attach to enzymes, they modify the enzyme's structure, generating a transitory intermediate with lower activation energy, allowing reactants to move closer to the product more quickly.
Induced fit in macromolecules displays changes in macromolecule shape in response to ligand binding as the macromolecule's binding site conforms efficiently to the ligand's shape.