Faceting refers to the relative coarseness or smoothness of a curved area. Most CAD packages allow you to control faceting through chord height, angle control and angle tolerance. Excessively fine faceting will ensure a smooth surface area but is likely to increase build times and production costs. Coarse faceting will lower production costs and build times however is likely to result in flat surfaces rather than smooth curves, for example a heavily faceted file of a pound coin would most likely create a coin similar in shape to a fifty pence piece. Ideally to keep build times and costs to a minimum without compromising on surface finish your file should be just detailed enough to allow required features to build while maintaining a manageable file size.