Difference between logs, timber, and lumber

I'm interested in the distinctions between these three terms. Here's what I already know: timber is wood that is still attached to the ground, and still has its bark on. Lumber is already felled, and no longer has its bark. [source]

But my question is, does lumber refer to wood that is already processed into boards and planks? Or does it refer to felled wood that has not yet been processed into boards and planks?

It might make more sense to pull up a few definitions for these nouns:

Log:

• "1. A rough bulky piece of timber unhewed; a block; a piece of wood." (Lloyd's Encyclopædic dictionary, Vol. 4, 1895, page 626, "lœwigite—loganite")

• "1. A section of the trunk or of a large branch of a felled tree, either in its natural state or cut up for use in building, as firewood, etc." (Webster's New World College Dictionary, as provided by the Associated Press Stylebook Online, 2015-04-14)

Lumber:

• "7. Marketable Timber." (Lloyd's Encyclopædic dictionary, Vol. 4, 1895, page 668, "lumbaginous—lump")

• "2. Timber sawed into beams, planks, boards, etc. of sizes convenient for building or carpentry." (Webster's New World College Dictionary, as provided by the Associated Press Stylebook Online, 2015-04-14)

Timber:

• "Trees cut down, squared, or capable of being squared, into beams, rafters, boards, planks, etc., to be employed in the construction of houses, ships, etc., or in carpentry, joinery, etc." (The American Encyclopædic Dictionary, Vol. 4, 1896, page 4096, "tilly—timber")

• "2. Wood suitable for building houses, ships, etc., whether cut or still in the form of trees." (Webster's New World College Dictionary, as provided by the Associated Press Stylebook Online, 2015-04-14)

So what we can get from these definitions is that timber is the tree or trees that were planted in a grove for the purpose of cutting or found in a forest, which, when cut down, could then further be cut up into various useful pieces of wood that could then be used in building various projects, such as houses or ships.

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Lumber is the wood, already cut to any marketable size — from boards meant for flooring, to rafters and beams meant for holding up a structure. If you went to a Home Depot, or another large home-improvement store, you would usually buy the marketable bits of wood here in the lumber department.

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Logs are the piece of a felled tree, usually the size of a large branch (could even be a large branch) up to a whole section of a trunk, and generally just a rough piece of wood that you could use either as-is (such as in building a log cabin), for use in small-to-medium projects, or to be used as firewood. Not generally to be found in a finished and marketable form such as a board or plank, which would be lumber. However logs can be marketed and sold as logs, just not as lumber.

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When you have a tree that is standing in nature, unharmed, its called timber.

When they cut down the tree, they also remove the branches from it. The tree as it is now is called lumber. A lumber is basically a long tree without its roots and all branches removed. Usually it still has the barks on.

In this form, it can be moved to a facility for processing.