The symbol
used to indicate a root is called a radical, or sometimes a surd.
The expression
is therefore read "
radical ," or "the nth
root of ."
In the radical symbol, the horizonal line is called the vinculum,
the quantity under the vinculum is called the radicand,
and the quantity
written to the left is called the index.

In general, the use of roots is equivalent to the use of fractional exponents
as indicated by the identity

(1)

a more generalized form of the standard

(2)

The special case
is written
and is called the square root of .
is called the cube root.

Some interesting radical identities are due to Ramanujan, and include the equivalent forms