LaTeX internal “abbreviations”, etc.

In the deeps of time, when TeX first happened, computers had extremely limited memory, and were (by today’s standards) painfully slow. When LaTeX came along, things weren’t much better, and even when LaTeX 2e appeared, there was a strong imperative to save memory space (and to a lesser extent) CPU time.

From the very earliest days, Knuth used shortcut macros to speed things up. LaTeX, over the years, has extended Knuth’s list by a substantial amount. An interesting feature of the “abbreviations” is that on paper, they may look longer than the thing they stand for; however, to (La)TeX they feel smaller…

The table at the end of this answer lists the commonest of these “abbreviations”. It is not complete; as always, if the table doesn’t help, try the LaTeX source. The table lists each abbreviation’s name and its value, which provide most of what a user needs to know. The table also lists the abbreviation’s type, which is a trickier concept: if you need to know, the only real confusion is that the abbreviations labelled ‘defn’ are defined using an \xxxxdef command.

Name Type Value
\m@ne count -1
\p@ dimen 1pt
\z@ dimen 0pt
\z@skip skip 0pt plus 0pt minus 0pt
\@ne defn 1
\tw@ defn 2
\thr@@ defn 3
\sixt@@n defn 16
\@cclv defn 255
\@cclvi defn 256
\@m defn 1000
\@M defn 10000
\@MM defn 20000
\@vpt macro 5
\@vipt macro 6
\@viipt macro 7
\@viiipt macro 8
\@ixpt macro 9
\@xpt macro 10
\@xipt macro 10.95
\@xiipt macro 12
\@xivpt macro 14.4
\@xviipt macro 17.28
\@xxpt macro 20.74
\@xxvpt macro 24.88
\@plus macro plus
\@minus macro minus