Open space

What is this term "open space" that we use so freely...does anyone know the origins?
thanks

From sense #8 of "open" as an adjective, Oxford English Dictionary:

"Of a passage or space: Not occupied by anything that prevents passage or view; free from obstructions; unobstructed, clear. Of a country: Free from wood, buildings, etc. Of a river, port, etc.: Not frozen over, free from ice."

The OED's quotations containing "open" in this sense as applied to various kinds of settings start at the year 1400. Here are some that are more specifically applicable to "space":
"The country was all open, with very little wood, and no trees" .
""The Preservation of Open Spaces and of Footpaths and Other Rights of Way" (title; 1896).