In C++, a variable is a named storage location in a computer's memory that is used to hold a value of a particular data type. Variables are used to store values that are used by a program, such as numbers, strings, and objects.

When you declare a variable in C++, you specify its name and data type. For example, you could declare an integer variable named "myNumber" like this:

int myNumber;

This declares a variable of type "int" (short for integer) named "myNumber". The variable can be assigned a value like this:

myNumber = 42;

Alternatively, you can declare and initialize a variable in a single statement like this:

int myNumber = 42;

Once a variable has been declared and initialized, it can be used in expressions, assignments, and other statements throughout the program. For example, you could use the variable in a calculation like this:

int result = myNumber * 2;