Terra firma means ‘dry land.’
Terra firma is a New Latin term literally meaning ‘solid earth.’ It’s first recorded use in the English language was c. 1595-1605.
Terra firma is not used to mean Earth in general, as opposed to space; just dry land, that is, the solid part of the earth.
Compared to other New Latin terms, the use of terra firma is considerably rare, although it is recognisable to many people. Examples of use in a sentence include:
‘Bob couldn’t wait to get his feet back on terra firma when his cruise had finished.’
‘The sailors returned to terra firma to meet their families after months out in the sea.’