This is the direction in which the wood cell fibers grow. These variances in grain direction can have a significant impact on the project you're working on. The grain direction is important to consider when building both structural projects or decorative projects such as furniture or crafts. For instance, when working on a structural application, a straight-grained board is generally the strongest. In more decorative projects, grain with varying characteristics can add beauty and personality to your final result.
Grain pertains to the wood-cell fibers' orientation.
And the kind of project you're undertaking will dictate the type of grain most suitable. When a straight-grained log is not sawn along its vertical axis, diagonal grain is the result. When trees grow twisted, spiral-grained logs and subsequent boards are produced. The board's fibers run approximately parallel with the vertical axis of the log from which it originated. This type of grain results when the direction of wood fibers has constantly changed.