Means the absence of any other  essential oils that can blend, stretch, dilute or extend the oil (i.e. Lavender extended with Lavandins). Pure essential oil is just that - it is pure - and unadulterated.

The oil has not been tampered with. No decolorizing, recolorizing or deterpenization. Complete means essences are not decolorized, recolored, or deterpenated. Deterpenating results in lower bioactivity (Thyme becomes more toxic, Lavender has catalyst values taken away.)