Garden Tubs
Garden Tubs are so named to suggest the serenity of a country garden.

In 18th century France, tubs were actually sometimes placed in the gardens of wealthy landowners as depicted in this antique zinc model.
When they were drained, the water fed the vegetation.
Legend has it that later, luxury homes in England built baths that overlooked the gardens surrounding the estate, in rooms that came to be called "garden rooms." They are roughly equivalent to what today might be called a "sun room."

The term, "garden tub," is more common in certain regions, but there is little consensus. For awhile, the term was used for any tub installed under or near a window that looked out onto the landscape.
In practice, the term usually refers to a larger, deeper tub, without an integrated shower or whirlpool jets, and is used for soaking only.
However, the words "gargen tub" carries such pleasant connotations that it has been borrowed to apply to virtually any tub, and has consequently ceased to have any real meaning.