A covalent bond is a type of chemical bond in which atoms share pairs of electrons to achieve stability.

More specifically, a covalent bond represents one of the fundamental types of bonding that occurs between atoms. This chemical linkage is characterized by the sharing of one or more pairs of electrons between atoms. By sharing electrons, each atom can attain a stable electron configuration akin to that of a noble gas.

Covalent bonds typically form between two non-metal atoms that possess similar electronegativities. Both atoms require additional electrons to achieve stability. Unlike ionic bonding, where electrons are transferred from one atom to another, covalent bonding involves the sharing of electrons. For instance, two hydrogen atoms can form a covalent bond to create a hydrogen molecule, denoted as $H_2$, by sharing their single electrons.

The number of covalent bonds that an atom can form is generally determined by the number of electrons needed to complete its outer shell. For example, carbon, which has four electrons in its outer shell, can form four covalent bonds with other atoms.

Covalent bonds can be classified as single, double, or triple bonds, depending on the number of electron pairs being shared. For instance, oxygen atoms can form a double bond, as seen in $O_2$, by sharing two pairs of electrons.

Covalent bonding leads to the formation of molecules or molecular compounds. These compounds exhibit various properties based on the atoms involved and the structure of the molecule. For example, water ($H_2O$) exists as a liquid at room temperature, while carbon dioxide ($CO_2$) is a gas, despite both being covalently bonded molecules.

In summary, covalent bonding is a pivotal concept in chemistry that underpins the structure and properties of numerous substances. It involves the sharing of electron pairs between atoms, resulting in the formation of molecules with a wide range of characteristics.