Unbreakable block

See Preventing page breaks between lines in the UK TeX FAQ. Basically, you may use one of the following:

• the samepage environment;
• a \parbox or a minipage;
• the \needspace command of the package of the same name.

You may also need "to accept that not everything can be accomplished totally automatically".

A \vbox (or \vtop) will never be broken across pages:

\vbox{%
  Text here will not split over pages, it will remain
  as one continuous chunk. If there isn't enough room
  for it on the current page a pagebreak will happen
  before it and the whole chunk will start on the next
  page.}

(unless you \setbox it, and later \unvbox it)

You can also use packages to create and format the environment via options:

• package adjustbox
• package mdframed with the option nobreak
• package tcolorbox