{environments} is for general questions related to (La)TeX environments. For questions about environment subcategories like {lists}, {quoting} environments, or {floats} use the appropriate tag instead.
LaTeX environments start with \begin{name} and end with \end{name}.
In TeX environments may start with \name and end with \endname.
ConTeXt environments start with \startname and end with \stopname.
(Here name represents the actual environment name.)
LaTeX environments can be defined, redefined or provided (i.e. only defined when they don't exist yet) using:
\newenvironment{<name>}{<code at begin>}{<code at end>}
\renewenvironment{<name>}{<code at begin>}{<code at end>}
\provideenvironment{<name>}{<code at begin>}{<code at end>}
