Tab order is the order in which the user can move from one item to another item on a page using the Tab key. Filling in a form is much faster and easier if the user only has to press Tab to jump to the next item in a logical sequence.
Tab order is also referred to as Next tab order.Previous tab order is the order in which the user can move from item to item on a page by pressing Shift+Tab. Previous tab order is often the opposite of next tab order; however, it is possible to set up next tab order and previous tab order so they are unrelated to each other.
When you insert items onto a page, the Designer automatically defines the tab order as the order in which you insert the items. (In other words, the default tab order is the same as the build order. In addition, the default previous tab order is the opposite of the default next tab order.) Unless you plan your form very well, this tab order will rarely be ideal. However, you can modify the tab order at any time.