$ContextPath is a global variable that gives a list of contexts, after $Context, to search in trying to find a symbol that has been entered.

$KernelID is a unique ID number assigned to each running parallel kernel.

$MaxPrecision gives the maximum number of digits of precision to be allowed in arbitrary-precision numbers.

$Pre is a global variable whose value, if set, is applied to every input expression.

$PreRead is a global variable whose value, if set, is applied to the text or box form of every input expression before it is fed to Mathematica.

$ProcessorCount gives the number of processor cores available on the computer system on which Mathematica is being run.

$UserBaseDirectory gives the base directory in which user-specific files to be loaded by Mathematica are conventionally placed.

In many kinds of numerical computations, it is convenient to introduce approximate functions. Approximate functions can be thought of as generalizations of ordinary ...

You can do arithmetic with Mathematica just as you would on an electronic calculator. This is the sum of two numbers. Here the / stands for division, and the ^ stands for ...

When you manipulate power series, it is sometimes convenient to think of the series as representing functions, which you can, for example, compose or invert. Composition and ...