"Poke your finger into the clock; fiddle the escape wheel (every part perfectly named – escape: the end of the machine, the place where the energy leaks out, breaks free, beats time)."
Anchor and Escape Wheel of a Late Nineteenth Century Clock
Creative Commons Attribution Share AlikeAnchor and Escape Wheel of a Late Nineteenth Century Clock - Credit: Timwether

The escape wheel is a part of the “escapement”, which is  controlled by the periodic swing of the pendulum or balance wheel. It is powered by a coiled spring or suspended weight that rotates a gear train. The escapement allows the gears to advance or "escape" a fixed amount with each swing, to move the timepiece's hands forward at a steady rate. It regulates the clock’s system, so that it doesn’t unwind uncontrollably.

The jeweled pallets and escape wheel teeth are particularly elegant in this video of a Brocot escapement in a French mantel clock.