If you're spineless, you're weak or cowardly — or both.

What does it mean if a person is spineless?

having no spine or backbone. having a weak spine; limp. without moral force, resolution, or courage; feeble: a spineless, lily-livered coward.

What does it mean to be called weak?

If you describe someone as weak, you mean that they are not very confident or determined, so that they are often frightened or worried, or easily influenced by other people.