Timber

Lumber (American English; used only in North America) or timber (used in the rest of the English-speaking world) is a type of wood that has been processed into beams and planks, a stage in the process of wood production. Lumber is mainly used for structural purposes but has many other uses as well.

There are two main types of lumber. It may be supplied either rough-sawn, or surfaced on one or more of its faces. Besides pulpwood, rough lumber is the raw material for furniture-making and other items requiring additional cutting and shaping. It is available in many species, usually hardwoods; but it is also readily available in softwoods, such as white pine and red pine, because of their low cost.

Finished lumber is supplied in standard sizes, mostly for the construction industry – primarily softwood, from coniferous species, including pine, fir and spruce (collectively spruce-pine-fir), cedar, and hemlock, but also some hardwood, for high-grade flooring. It is more commonly made from softwood than hardwoods, and 80% of lumber comes from softwood.

Terminology
In the United States milled boards of wood are referred to as lumber. However, in Britain and other Commonwealth nations, the term timber is instead used to describe sawn wood products, like floor boards.

In the United States and Canada, generally timber describes standing or felled trees. Specifically in Canada, lumber describes cut and surfaced wood. 

In the United Kingdom, the word lumber is rarely used in relation to wood and has several other meanings, including unused or unwanted items. Referring to wood, Timber is almost universally used instead.

Conversion of wood logs
Logs are converted into timber by being sawn, hewn, or split. Sawing with a rip saw is the most common method, because sawing allows logs of lower quality, with irregular grain and large knots, to be used and is more economical. There are various types of sawing:

• Plain sawn (flat sawn, through and through, bastard sawn) – A log sawn through without adjusting the position of the log and the grain runs across the width of the boards.
• Quarter sawn and rift sawn – These terms have been confused in history but generally mean lumber sawn so the annual rings are reasonably perpendicular to the sides (not edges) of the lumber.
• Boxed heart – The pith remains within the piece with some allowance for exposure.
• Heart center – the center core of a log.
• Free of heart center (FOHC) – A side-cut timber without any pith.
• Free of knots (FOK) – No knots are present.

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https://en.wikipedia.org/wiki/Lumber