Keywords also know as reserved words. In programming terms these are words saved for use by the compiler as a individual token with a strict meaning. They are reserved because they are given a special meaning. They cannot be reassigned or redefined to a new meaning.

Keywords List for different ANSI programming languages.

auto break case char
const continue default do
double else enum extern
float for goto if
int long register return
short signed sizeof static
struct switch typedef union
unsigned void volatile while

ANSI Standard Pascal
and array begin case
const div do downto
else end file for
function goto if in
label mod label mod
nil not of or
packed procedure program record
repeat set then to type
until var while with

While Java does not yet have a ANSI standard this list comes from sun list of keywords.
abstract double int strictfp
boolean else interface super
break extends long switch
byte final native synchronized
case finally new this
catch float package throw
char for private throws
class goto protected transient
const if public try
continue implements return void
default import short volatile
do instanceof static while

C++ also does not yet have offical have a ANSI standard. However this list comes from the public view document called "Proposed International Standard for Information Systems Programming Language C++ by the C++ standardization committees"
asm do inline short
typeid auto double int
signed typename bool dynamic
cast long sizeof union
break else mutable static
unsigned case enum namespace
static_cast using catch
explicit new struct virtual
char extern operator switch
void class false private
template volatile const float
protected this wchar_t
const_cast for public throw while
continue friend register true
default goto reinterpret_cast try
delete if return typedef