rules and borders
In traditional printing terminology, a rule is a line; a border is a box. But in word processors, they’re variations of the same function. Rules and borders can be applied to pages, paragraphs, or tables.
Like centered text, bold or italic, and all caps, rules and borders are best used sparingly. Ask yourself: do you really need a rule or border to make a visual distinction? You can usually get equally good results by adding space above and below. Try that first.
For borders, set the thickness between half a point and one point. Thinner borders can work on professionally printed goods but are too fine to reproduce well on an office printer. Thicker borders are counterproductive—they create noise that upstages the information inside. You want to see the data, not the lines around the data.