Lumber is wood after trees have been cut to standard sizes and now available for use. You go to a lumberyard to select lumber to build something. Timber refers to wood as trees. Where I live people will buy land for the timber. Meaning they log it(leaning to cut down) and take to a lumber mill to sell. There is it made into lumber.

None, really! Both are "business words" for talking about the wood industry. The only difference I can think of is that you can yell "Timber!" when something big is falling. Generally people associate someone yelling "timber!" with a tree falling, but in conversation it could refer to anything, really. You can't use "lumber!" in the same sense.

Timber is the word we use in Australia, Britain, and lumber is what Americans call the material. Trees are made from wood, and when the wood is processed it is called timber/lumber. The word "timber" is allied to 'zimmer' a room, 'dom/ дом" a house, and the "domestic" words that come from it. It infers a building material, not raw wood/logs. You can buy lumber in a lumberyard, but we call it here timber in a timber yard, but it's the same thing. Wood is a general word for the untreated, unprocessed raw material.