The Page Up and Page Down keys (sometimes abbreviated as PgUp and PgDn) are two keys commonly found on computer keyboard

Computer keyboard

In computing, a keyboard is a typewriter-style keyboard, which uses an arrangement of buttons or keys, to act as mechanical levers or electronic switches...

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The two keys are primarily used to scroll up or down in documents, but the scrolling distance varies between different applications. In cases when the document is shorter than one screenful, the Page Up and Page Down keys don't respond.

The arrow keys

Arrow keys

Cursor movement keys or arrow keys are buttons on a computer keyboard that are either programmed or designated to move the cursor in a specified direction....

 and the scroll wheel

Scroll wheel

A scroll wheel is a hard plastic or rubbery disc on a computer mouse that is perpendicular to the mouse surface. It is normally located between the left and right mouse buttons.- Functionality :...

 can also be used to scroll a document, although by smaller incremental distances.

In most operating systems, if the Page Up or Page Down key is pressed along with the shift key

Shift key

The shift key is a modifier key on a keyboard, used to type capital letters and other alternate "upper" characters. There are typically two shift keys, on the left and right sides of the row below the home row...

 in editable text, all the text scrolled over will be highlighted.

In some applications, the Page Up and Page Down keys behave differently in Caret navigation

Caret navigation

In computing, caret navigation is a kind of keyboard navigation where a caret is used to navigate within a text document...

(toggled with the F7 function key).