A google search for "yard" yielded this..

A google search for "garden" returned this..

As an American overseas, if I’ve heard this once, I’ve heard this ten times in the U.K… "Why do Americans refer to their outdoor planted spaces as yards?"  "Aren’t yards where cars are put up on blocks? Where railcars are stored?" 

Paul Groth writes in “The Meaning of Gardens”, “What does it mean that Americans chose to call their arrangements of cars parked outdoors as lots?  Why not carparks as in Canada and the U.K.  Why have we overtly fashioned no parking gardens, or at least parking yards?  Three of these terms – lot, yard and garden –denote a simple but important hierarchy in the way Americans organize their space.”

According to Merriam-Webster dictionary, here are the first seven definitions for the word "YARD":

1: a small, usually walled and often paved area open to the sky and adjacent to a building : a court

2: the grounds of a building or group of buildings

3: the grounds immediately surrounding a house that are usually covered with grass

4 : an enclosure for livestock (as poultry)

5: an area with its buildings and facilities set aside for a particular business or activity

6: an assembly or storage area (as for dry-docked boats)

7: a system of tracks for storage and maintenance of cars and making up trains

8: a locality in a forest where deer herd in winter

On Wiktionary… a yard is a small, usually uncultivated area adjoining or (now especially) within the precincts of a house or other building, An enclosed area designated for a specific purpose, e.g. on farms, railways etc.

In Jamaica, "yard" is vernacular for “one’s house or home."

"Lot" stands as one of the oldest words for a division of land. "Yard" denotes more enclosure, or an area for special work, business or storage. Or, lack of attention as in “open lot” and “vacant lot”.  Groth associates the notion of “yard” with barns, prisons, ships, etc.  In fact, the word harkens back to the 12th century middle English as a word for enclosure.

In terms of organizing open space design, there is a hierarchy of meaning within “lot,” “yard,” and “garden.” Lot is commonly used in real estate terms, historically it equates to a division of land. This is an enclosure.

“We define lots or yards by their edges and their neighboring spaces; lots and yards hold something else. The garden is defined by what is in it. Its immediate meaning derives largely from itself and its contents.”

There is also a hierarchy of care, cultivation and pleasure among these three words. “The word ‘yard’ implies more value than something called a ‘lot’, in turn, the word ‘garden’ suggests something treasured.”

Gardens provide delight and amusement. Its contents are aesthetically pleasing and it is not defined by it’s edges, but rather by it’s contents. The term "pleasure garden" never referred to a yard or lot. Henceforth, lets turn yards into gardens." --The Meaning of Gardens: Francis and Hester, MIT Press, 1990.

Photos: lot/NYTimes, yard/sgvtribune.com, garden/lowcrapdiet.com