Jojoba esters are a mixture of various wax esters from jojoba oil. They are used in skincare products as fantastic emollients and occlusive moisturizing agents that won't leave a sticky, oily feeling on the skin.
They are especially beneficial for the skin when mixed with glycerin in the skincare formula. On dry skin, this ingredient acts as a soothing emollient that relieves itchiness and flakiness.
Esters are created when a fatty acid and fatty alcohol are joined together with a chemical bond. Jojoba oil (or more correctly, jojoba wax) is naturally comprised of these esters instead of triglycerides like most oils. These jojoba esters can be used in their native state or can be chemically modified by hydrogenation or interesterification (which breaks down the ester bond and then re-makes it again with a random combination of fatty acids and fatty alcohols, which makes the jojoba esters more homogenous).
Depending on the processing, jojoba esters can be liquid, semi-solid, or solid and wax-like.
Read more about jojoba oil here: Simmondsia Chinensis (Jojoba) Seed Oil.