The term "elementary" or "fundamental" is used to describe the charge of the electron (denoted as e) because it is the smallest known unit of electric charge that has been observed in isolated particles. The charge of an electron is considered to be indivisible within the framework of current particle physics theories.
Quarks, which are elementary particles that make up protons and neutrons, do indeed carry fractional charges. There are six known types, or flavors, of quarks: up, down, charm, strange, top, and bottom. The up and down quarks, which are the lightest and most common, have charges of +2/3e and -1/3e, respectively.
While quarks do have fractional charges, they are not observed as isolated particles due to a property called color confinement. Quarks are always found in combinations of three, called baryons (such as protons and neutrons), or in pairs with their antimatter counterparts, called mesons. These combinations ensure that the resulting composite particle has an overall integer charge.
It's worth noting that the fractionally charged quarks are confined within hadrons (baryons and mesons) and cannot be directly observed as free particles. In the context of electric charge, the elementary charge of the electron remains the smallest known indivisible unit that has been experimentally observed.
The fact that quarks have fractional charges is an interesting aspect of particle physics, but it does not negate the designation of the electron's charge as "fundamental" or "elementary" within the context of isolated particles.