Question

Bias by omission includes

Answer 1

Omission bias is the tendency to judge harmful actions as worse, or less moral than equally harmful inactions because actions are more obvious than inactions.

Answer 2

Bias by omission includes intentionally leaving out key information.
If you are biased, it means you are partial to something - it is some sort of unreasonable like or dislike towards somebody or something. So here, bias by omission means that you are not including some details because you don't want them to be seen, or something like that.