Encourage or discourage a page break. The optional zero-to-four
is an integer that allows you to soften the request. The default is 4,
so that without the optional argument these commands entirely force or
prevent the break. But for instance
\nopagebreak suggests to
LaTeX that another spot might be preferable. The higher the number,
the more insistent the request. Both commands are fragile
LaTeX’s page endings are optimized so ordinarily you only use this command in a document body to polish the final version, or inside commands.
If you use these inside a paragraph, they apply to the point following the line in which they appear. So this
Four score and seven years ago our fathers brought forth on this continent, \pagebreak a new nation, conceived in Liberty, and dedicated to the proposition that all men are created equal.
does not give a page break at ‘continent,’ but instead at
‘nation,’ since that is where LaTeX breaks that line. In
\pagebreak the vertical space on the page is
stretched out where possible so that it extends to the normal bottom
margin. This can look strange, and if
\flushbottom is in effect
this can cause you to get ‘Underfull \vbox (badness 10000) has
occurred while \output is active’. See \newpage for a command that
does not have these effects.