Felling
The operation of cutting down a standing tree so that it falls in a controlled direction. It is done with a directional notch on the intended fall side and a back cut that leaves an uncut hinge of wood to steer the tree.
Felling is by a wide margin the most dangerous chainsaw task and the one most deserving of formal training rather than a written summary. The essentials are assessing lean, crown weight, wind and rot before starting; clearing two escape routes at roughly 45 degrees behind the tree; cutting an accurate notch; and leaving a hinge of even thickness, because the hinge is the only thing that controls direction. Wedges or a felling lever prevent a tree from sitting back on the bar. Any tree that is hung up, leaning against another, or larger than your bar deserves a professional, not improvisation.