A caption is a numbered label, such as "Figure 1," that you can add to a table (table: One or more rows of cells commonly used to display numbers and other items for quick reference and analysis. Items in a table are organized into rows and columns.), figure, equation, or other item.

Label that you select
Number that Microsoft Word inserts for you
You can have Word automatically add captions when you insert tables, figures, or other items in your document. Or, if you've already inserted the items, you can add captions manually.
You can vary the caption label and number format for different types of items — for example, "Table II" and "Equation 1-A" — or you can change the label for one or more captions — for example, change "Table 6" to "Figure 6." You can also create a new caption label, such as "Photo." If you later add, delete, or move captions, you can easily update the caption numbers all at once.