A name (from the Greek anthrōpos for ‘human being’, and kainos for ‘new’) for the current (since around 1950) geological epoch. The idea is that humanity is now having such a profound influence on nature, including on global atmospheric composition and temperature, on the stability of ice and permafrost, on ocean chemistry through acidification, anoxia and pollution, on sea level through thermal expansion and ice melt, on biodiversity through mass extinction, and on landscape processes through erosion and sedimentation, that this will all be easily visible in the geological record all over the Earth for all future time. The Anthropocene thus brings to a sudden end the Holocene, a warm, stable interglacial (or as it may turn out, post-glacial) period that lasted for 11,700 years during which almost all recorded human history occurred.
Key reference: Waters, C.N., Zalasiewicz, J., Summerhayes, C., Barnosky, A.D., Poirier, C., Gałuszka, A., Cearreta, A., Edgeworth, M., Ellis, E.C., Ellis, M., Jeandel, C., Leinfelder, R., McNeill, J. R., Richter, D. deB., Steffen, W., Syvitski, J., Vidas, D., Wagreich, M., Williams, M., An, Z-S., Grinevald, J., Odada, E., Oreskes, N. & Wolfe, A.P. (2016) The Anthropocene is functionally and stratigraphically distinct from the Holocene. Science, 351 (6269): 138-141.