A Hadley Cell is an Atmospheric circulation pattern of upward motion at the equator a few kilometers, then toward the poles to about 30 degrees latitude (on Earth) then down to the surface and back to the equator. It was identified by George Hadley in the 18th century and explains the easterly Trade Winds at the base of the cell, because the flow toward the equator (e.g., north-to-south in the northern hemisphere) at the surface is deflected by the Coriolis Force (this deflection being called the Coriolis Effect). The term Hadley Circulation refers to the general circulation pattern including Hadley cells.
The Earth also has a Polar Cell or Polar Vortex, air rising closer to 60 degrees latitude, within the troposphere (to no more than 8 km), moving poleward and descending close to the pole.
The Earth also has a Ferrel Cell or Zone Of Mixing, a circulation pattern joining the two: some of the air rising as per the polar cell splitting from it, moving southward and descending with the current of the Hadley cell, then returning northward to rejoin the polar cell. It was first theorized by William Ferrel in the 19th century. Analogously associated with it are the winds known as the Westerlies.
These are useful elements in models of weather on other planets and Moons. Their existence and extent varies based on the size of the body and its Frequency of rotation. Titan's circulation is basically just a Hadley cell extending to its polar region. Jupiter, with a faster rotation, is divided north/south into more of these sorts of cells.
Intertropical Convergence Zone (ITCZ)
One Dimensional Climate Model