In C++, a structure is a user-defined data type that groups together related data items of different data types. A structure can contain any combination of primitive data types, other structures, pointers, and arrays.

To define a structure in C++, you can use the struct keyword followed by the name of the structure and a set of braces that enclose the structure members. For example:

struct Person {
    std::string name;
    int age;
    double height;
};

In this example, we define a Person structure that contains three members: a std::string object named name, an integer variable named age, and a double variable named height.

Once the structure is defined, you can create variables of that structure type by using the struct keyword followed by the structure name, as shown below:

Person p1; // create a variable of type Person

You can also initialize the members of the structure at the time of creation using a set of braces that contain the member values, as shown below:

Person p2 = {"John", 25, 1.75}; // create a variable of type Person and initialize its members

You can access the members of a structure variable using the dot operator (.) followed by the member name, as shown below:

p1.name = "Jane";
p1.age = 30;
p1.height = 1.65;

In this example, we set the values of the name, age, and height members of the p1 variable.