Introduction:
A variable is a fundamental concept in programming and is used to store and manipulate data. It acts as a placeholder that can hold different values during the execution of a program. In this question, the statement "A variable is a placeholder for some value" is true.

Explanation:
- What is a variable?
- A variable is a named storage location in a computer's memory where data can be stored and retrieved.
- It has a unique name that is used to reference and access the data it holds.

- Why do we use variables?
- Variables allow us to store and manipulate data in a program.
- They provide a way to refer to specific data without directly specifying its value.
- By using variables, we can write reusable and flexible code that can work with different values.

- How are variables used?
- Declaration: Before using a variable, we need to declare it. This involves specifying the variable's name and its data type.
- Initialization: After declaring a variable, we can assign an initial value to it. This is called initialization.
- Assignment: Once a variable is declared and initialized, we can assign new values to it as needed.
- Usage: Variables are used in expressions, calculations, and manipulations to perform various operations.

- Examples:
- In a simple program that calculates the area of a rectangle, we can use variables to store the values of length and width:
```
int length = 5; // declaring and initializing length variable
int width = 3; // declaring and initializing width variable
int area = length * width; // calculating area using variables
```
- In this example, the variables "length" and "width" act as placeholders for the values 5 and 3 respectively. The variable "area" holds the result of the calculation.

Conclusion:
In summary, a variable is indeed a placeholder for some value. It allows us to store and manipulate data in a program and provides flexibility and reusability to our code. By using variables, we can write more efficient and dynamic programs.