\math...: examples are
\mathbf, \mathcal, etc.
\text...: e.g. \textbf and \textrm. The exception to this is
\emph, since it occurs very commonly in author documents and so
deserves a shorter name.
The LATEX3 project reserves the use of encodings starting with the
following letters: T (standard 256-long text encodings), TS
(symbols that are designed to extend a corresponding T encoding),
X (text encodings that do not conform to the strict requirements for
T encodings), M (standard 256-long math encodings), S (other
symbol encodings), A (other special applications), OT (standard
128-long text encodings) and OM (standard 128-long math encodings).
Please do not use the above starting letters for non-portable encodings. If new standard encodings emerge then we shall add them in a later release of LATEX.
Encoding schemes which are local to a site or a system should start
with L, experimental encodings intended for wide distribution will
start with E, whilst U is for Unknown or Unclassified encodings..
\text followed by
the Adobe glyph name: for example \textonequarter or
\textsterling. Similarly, math symbols should be named as
\math followed by the glyph name, for example \mathonequarter
or \mathsterling. Commands which can be used in text or math can
then be defined using \ifmmode, for example:
\DeclareRobustCommand{\pounds}{%
\ifmmode \mathsterling \else \textsterling \fi
}
Note that commands defined in this way must be robust, in case they
get put into a section title or other moving argument.