Steric strain refers to the repulsion between atoms or groups within a molecule that occurs when they are forced closer together than their preferred distance. This strain arises from the physical size of the atoms or groups, which can lead to increased energy and instability in the molecule. In organic chemistry, steric strain is particularly important in determining the stability of conformers and isomers. For example, bulky groups in a cycloalkane can create steric strain, making certain conformations less favorable. Understanding steric strain helps chemists predict molecular behavior and reactivity.