Reserved words

if
then
else
about
and
animate
as
at
by
case
catch
collect
continue
coordsys
do
exit
fn
for
from
function
global
if
in
local
macroscript
mapped
max
not
on
or
parameters
persistent
plugin
rcmenu
return rollout
set
struct
throw
to
tool
try
undo
utility
when
where
while
with

predefined constants/literals:

true/false
on/off
pi
e
red
green
blue
black
yellow
orange
white
grey
brown
x_axis
y_axis
z_axis
ok
undefined
dontcollect
unsupplied

There are also a number of global variables/constants that are defined for and accessible via maxscript. You can get a full list here using the following links:

http://docs.autodesk.com/3DSMAX/16/ENU/MAXScript-Help/index.html?url=files/GUID-914BC0D0-CC30-4B72-849D-5D34205B985D.htm,topicNumber=d30e34835

http://docs.autodesk.com/3DSMAX/16/ENU/MAXScript-Help/index.html?url=files/GUID-914BC0D0-CC30-4B72-849D-5D34205B985D.htm,topicNumber=d30e34835