# Variable

URL: https://softwaredictionary.org/terms/variable
Category: Programming Fundamentals
Last updated: 2026-09-29
In Turkish: Değişken

In short: A variable is a named storage location in a program that holds a value, such as a number or a piece of text, which the code can read and change as it runs.

## What is a variable?

A variable gives a name to a piece of data so your code can refer to it later. Instead of repeating the value 0.2 everywhere, you can store it in a variable called `taxRate` and use that name. The name makes code easier to read, and changing the value in one place updates it everywhere it is used.

A useful analogy for a variable is a labeled box. The label is the variable's name, and the thing inside the box is its value. Behind the scenes, the program reserves a spot in memory for the value and uses the name to find it again.

Most languages have rules about what a variable can hold and where it can be used. Its type, such as number, string, or boolean, determines which operations make sense, and its scope determines which parts of the code can see it. In JavaScript, `let` declares a variable that can be reassigned, while `const` declares one that cannot.

Variables are often confused with constants. A constant is a name bound to a value that should not change after it is set, while a regular variable is expected to change. In JavaScript, `const` prevents reassignment but does not freeze an object's contents, so the properties of a `const` object can still be modified.

## Key takeaways

- A variable is a name that points to a stored value.
- Its value can usually be read and changed while the program runs.
- Type controls what kind of data it holds; scope controls where it is visible.
- In JavaScript, use `const` by default and `let` when the value must change.

## Example: Declaring variables in JavaScript

```javascript
// let: the value can change later
let score = 0;
// const: the name can't be reassigned
const playerName = "Ada";

score = score + 10;             // update the value
console.log(playerName, score); // "Ada" 10

// playerName = "Bob"; // TypeError: Assignment to constant variable
```

## Frequently asked questions

**What is the difference between let, const, and var in JavaScript?**

`let` and `const` are block-scoped, meaning they only exist inside the nearest pair of curly braces, and `const` cannot be reassigned. `var` is the older, function-scoped keyword and is generally avoided in modern code because its scoping rules can cause surprising bugs.

**What is variable scope?**

Scope is the region of code where a variable can be accessed. A variable declared inside a function is local to that function, while one declared at the top level of a program may be visible everywhere, which is called global scope.

**What is the difference between a variable and a constant?**

A variable's value is expected to change while the program runs, while a constant is set once and should never change. Many style guides write true constants in uppercase, such as `MAX_USERS`, to make them easy to spot.

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Software Dictionary: https://softwaredictionary.org/ · https://softwaredictionary.org/llms.txt