What is definition of mass of a star?

Same as any other mass. The mass is sometimes (informally) described as the "amount of substance" something has.

Same as any other mass. The mass is sometimes (informally) described as the "amount of substance" something has.

Same as any other mass. The mass is sometimes (informally) described as the "amount of substance" something has.

Same as any other mass. The mass is sometimes (informally) described as the "amount of substance" something has.