typedef

typedef -- standard in C/C++. Used to assign a more meaningfull or appropriate name to a variable type. For instance you may be using int's as booleans, so why not declare them as booleans?

typedef old type new type;
typedef int bool;
typedef float dollars;
typedef struct box_t BoxDim;

now you can declare:
bool bHouseOnFire;
dollars dPrice;
BoxDim bMyBox;

Typedef is a language construct in C and therefore also in C++.
It has two main purposes:

• To name a complicated (composite) type with a simpler name
• To hide an implementation detail from other parts of implementation - as a handle where the actual type can easily be changed.

The last is especially important in C++ typedef, where a typedef can be a class member.

In most cases, typedef's use could be easily replaced by a #define. However, it allows the use of standard declaration and greater flexibility in more complicated cases.

With typedef, you can create types that are arrays, which would be unwieldy to do with #define:
    typedef int arrayType[5];
    arrayType array1;
As opposed to:
    #define arrayMacro(var) int var [5]
    arrayMacro(array2);

Another difference is scope - in gcc, typedefs defined in a function are not valid outside a function. However, a #define will be valid from the point of its definition to the end of the file.
In Microsoft Visual C++, you cannot define a typedef inside a function.

Also, typedefs and variables can have identical names. This could lead to some confusion for others trying to read the code, though.