In Kotlin, Compose is a modern UI toolkit for building native Android user interfaces. Compose modifiers are functions or methods that allow you to modify the behavior or appearance of a Compose UI component. They are used to apply transformations, define layouts, or add interactivity to the components.

Compose modifiers can be applied to Compose UI components using the Modifier class. This class provides a set of modifier functions that you can chain together to achieve the desired effects. Some commonly used modifiers include:

1. padding: Adds padding around the component.
2. fillMaxWidth and fillMaxHeight: Expands the component to occupy the maximum available width or height.
3. clickable: Adds clickability to the component.
4. background: Sets the background color or drawable for the component.
5. align: Positions the component within its parent or aligns it with other components.
6. weight: Specifies the weight of the component in a weighted layout.

Here's an example of how you can use modifiers in Kotlin Compose:

@Composable
fun MyComponent() {
    Box(
        modifier = Modifier
            .fillMaxWidth()
            .padding(16.dp)
            .background(Color.Blue)
            .clickable { /* Handle click event */ }
    ) {
        Text("Hello, Compose!")
    }
}

In this example, the Box component is modified with the fillMaxWidth, padding, background, and clickable modifiers. These modifiers modify the behavior and appearance of the Box component, making it expand to fill the available width, adding padding, setting the background color to blue, and making it clickable.

Modifiers provide a flexible and declarative way to define the layout and behavior of UI components in Kotlin Compose.