What is a garden? Well, I am basically being asked to define a word with more words and before I do this I would like you to consider this quote.
"A word is like a drunken, dumb man, who feels what kind of liquor is in him but who is unable to express himself clearly about it."(italics original)- Paramhansa Yogananda
A word has a general accepted meaning so that we can express ourselves to another and have each other somewhat understand what we mean. While this is convenient and I am currently writing this based on this assumption (for you would not understand me if we didn't agree on these words' definitions), I think it can be very limiting to the human mind if we use labels and put concepts in boxes. Therefore I refuse to define this word for two reasons:
1. That we all have a general idea of what a garden is when the word is used casually; it is true different things come to mind for different people but they are similar enough to enable communication.
2. A word can mean anything if we wish it so, and for this reason I could say anything and be justified. Now, listing everything in the universe is a task that I would not enjoy, so I choose to list nothing instead.
If a textbook definition is desired, there are many books there to fufill your need. I would like to reiterate that I don't consider it pointless to define words because they enable us to come together at a base level and for some this is the only type of accepted level of connecting, I just think that in this case it is better to leave some mystery to the word so it can be continually reinvented.