What does frivolous meanfrivolous mean

Frivolous can mean:

1 - Something unimportant, petty as in they regard window shopping as a frivolous activity;

2 - Something that is not serious, for example: she always has frivolous remarks about my clothes;

3 - And it is used in law to state that an argument has no solid basis, for instance: They kept showing some frivolous pieces of evidence.