A sigma bond is a type of covalent bond formed when two atomic orbitals overlap directly between the nuclei of two atoms. This overlap allows for the sharing of electrons, creating a strong bond that holds the atoms together. Sigma bonds are the first bonds formed between two atoms and can occur in single, double, or triple bonds, with each bond contributing to the overall stability of the molecule. In a molecule, sigma bonds are essential for defining its shape and structure. They allow for free rotation around the bond axis, unlike pi bonds, which are formed from the side-to-side overlap of orbitals and restrict rotation. Understanding sigma bonds is crucial for studying chemical reactions and molecular interactions.