The letter F with a numeral, marking a programmable key.
An F followed by a numeral marks the function keys along the top of a keyboard. What each does is set by whatever software is running, which is what distinguishes them from keys that produce a character.
Marks the row of keys whose action is assigned by software rather than fixed by the keyboard, numbered from F1 upward.
Contexts: Software
On laptops the same physical keys usually carry a hardware function — display brightness, volume — reached with or without a modifier depending on a firmware setting.
Contexts: Software
The capital letter F — an upright stroke with two horizontal arms from its top half — followed by one or two numerals set at the same height.
A fuller structured visual breakdown is not yet documented for this symbol.
Both are used in software contexts.