Transport of heat and moisture by the movement of a fluid. In meteorology, the term specifically describes vertical transport of heat and moisture, especially by updrafts and downdrafts in an unstable atmosphere. "Convection" and "thunderstorms" are often used interchangeably, although thunderstorms are only one form of convection. CBS (towering cumulus clouds), and ACCAS (altocumulus castellanus) clouds all are visible forms of convection, but convection is not always made visible by clouds. Convection occurring without cloud formation is dry convection, while the visible convection processes are moist convection.
Wow. Those clouds really have some convection going on. Look how tall they are.