The most common type of forms have a fixed layout; that is, they have a predetermined layout, always with a fixed number of pages regardless of the amount of data available to fill it. For example, a course registration form that an end user can either print and fill by hand, or fill in Acrobat or Adobe Reader. When filled, the form retains its original layout and number of pages. Fields that are not filled remain empty. Conversely, if the amount of data is more that the form can hold, the form cannot expand to accommodate excess data. For example, if a course registration form has 5 rows where end users list their course selections, and enough data is available to fill 10 rows, only 5 rows can be filled. Similarly, if an end user lists only 2 course selections, you will still see 5 rows, 2 that are filled and 3 that are empty.
This form can be interactive, where an end user fills the form typically in Acrobat or Adobe Reader, or it can be non-interactive, where a server process merges the form with data from a data source. Similarly, LiveCycle Forms ES typically renders non-interactive forms that have a fixed layout to present information from a data source.
In addition to forms that have a fixed layout, you can define sections of the form that will expand and shrink in response to the amount of data that is merged when the form is rendered. You do this by wrapping various sections (groups of subforms) in subforms that are set to flow content. Then, at run time, only the subforms that are necessary for displaying the exact amount of data are instantiated.
This type of form has a flowable layout with a varying number of pages. The subforms adjust depending on the amount of data merged with the form when it is rendered, or the subforms expand when end users need to add more data. For example, you may decide to let end users add to the form the number of rows they need to list their selections, remove rows from the form, and then return the form data electronically. Depending on how many rows they add, the form may extend over two or more pages.
In LiveCycle Designer ES, you can also create forms that have a flowable layout for use with LiveCycle Forms ES. In this scenario, the form design is merged with data on LiveCycle Forms ES. For example, such forms as a telephone bill or credit card statement are typically non-interactive forms and designed to present users with information from a data source. Users then print these forms or store them electronically. These forms are sometimes referred to as server-side forms because the merging of the form design and data occurs at the server.
See also 

Form design layouts