bystander cell - bystander effect (fibroblasts)

[pirol]

Dear all

I was looking for a correct deffinition of the term: Bystander cell.
I didn't finde much, but I think I got a clue:

Bystander cells, are cell not involved in a process, but are affected by it. E.g. uninvolved T-cells or B-cells through cytokine secretion.
Is this correct? Does somebody have a more accurate deffinition?
Can fibroblasts be called bystander cells in terms of vaccination?

I also found the term: Bystander effect.
Does this mean the effect of the process on the uninvolved bystander cells, or the effect bystander cells do exert on other cells?

Thanks for your help!