According to the ActionScript language reference, the star type:

Specifies that a property is untyped. Use of the asterisk symbol for a type annotation is equivalent to using no type annotation. Expressions that read from untyped properties are considered untyped expressions. Use of untyped expressions or properties is recommended in the following circumstances:

But deferring type checking to runtime can highly impact the robustness of the application because the compiler is unable to assist the developer.

Noncompliant Code Example

var obj:*;  // Noncompliant
var foo:* = new Something();  // Noncompliant

Compliant Solution

var obj:Something;
var foo:Something = new Something();