In simple terms, graphene, is a thin layer of pure carbon; it is a single, tightly packed layer of carbon atoms that are bonded together in a hexagonal honeycomb lattice.
In more complex terms, it is an allotrope of carbon in the structure of a plane of sp2 bonded atoms with a molecule bond length of 0.142 nanometres. Layers of graphene stacked on top of each other form graphite, with an interplanar spacing of 0.335 nanometres.
It is the thinnest compound known to man at one atom thick, the lightest material known (with 1 square meter coming in at around 0.77 milligrams), the strongest compound discovered (between 100-300 times stronger than steel and with a tensile stiffness of 150,000,000 psi), the best conductor of heat at room temperature (at (4.84±0.44) × 10^3 to (5.30±0.48) × 10^3 W·m−1·K−1) and also the best conductor of electricity known (studies have shown electron mobility at values of more than 15,000 cm2·V−1·s−1). Other notable properties of graphene are its unique levels of light absorption at πα ≈ 2.3% of white light, and its potential suitability for use in spin transport.
Bearing this in mind, you might be surprised to know that carbon is the second most abundant mass within the human body and the fourth most abundant element in the universe (by mass), after hydrogen, helium and oxygen. This makes carbon the chemical basis for all known life on earth, so therefore graphene could well be an ecologically friendly, sustainable solution for an almost limitless number of applications. Since the discovery (or more accurately, the mechanical obtainment) of graphene, advancements within different scientific disciplines have exploded, with huge gains being made particularly in electronics and biotechnology already.