The word Pennsylvania literally translates to "Penn's Woods" or "Penn's Forest."
March 4, 1681: King Charles II signs the charter granting the territory to William Penn (the son). Penn had suggested "New Wales" then "Sylvania". The king inserted "Penn" — "Let it be called Pennsylvania, for thy father's sake."
The name was apt: the colony was ~90% forested in 1681 (oak, chestnut, pine, hemlock). Today, ~60% forest cover remains (16.6M acres).
Some think "Penn" refers to William Penn the founder. It actually honors his father, the admiral. The son preferred "Sylvania" alone.