Sure! Here is a SEO friendly HTML response for the Scala interview question:

```html

What is the difference between vals, vars, and defs in Scala?

In Scala, vals are used for defining immutable variables, while vars are used for defining mutable variables. On the other hand, defs are used for defining methods or functions in Scala.

Val Example:
val x = 10
Once assigned, the value of x cannot be changed.

Var Example:
var y = 20
The value of y can be changed later on.

Def Example:
def add(a: Int, b: Int): Int = a + b
Defines a method add that takes two integers as input and returns their sum.

While vals and vars are used for defining variables, defs are used for defining executable code blocks.

```

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