A secondary logo can mean many things. And sometimes it can mean something completely different if the person doing the asking doesn’t know what they are asking for. Like on a crowdsourced logo site for example.
Is it a logo for a company, then secondary logos for each of their product lines (think Microsoft or Adobe.)
Is it a logo for a company with a vector lock-up then a blingd version for internet usage and spectacular printed stuff?
Is it a person asking for a vector lock-up then a B&W or W&B logo for use when needed.
Is it a person asking for a stacked logo and a horizontal logo?
That is why designers ask questions when they take on a client. Something sorely lacking in those crowdsource sites.