What does the word frivolous mean?

Frivolous:

1.) Characterized by a lack of seriousness or sense

2.) self-indulgently carefree; unconcerend about or lacking any serious purpose.

3.) (of a person) given to trifling or undue levity: a frivolous, empty-headed person.

4.) of little or no weight, worth, or importance; not worthy of serious notice.