Original Search Engine

Hi,

We are trying to do a report based on Original Search Phrase and Original Search Engine and am a bit confused on how it's populated. I thought this was limited to organic search, or paid search phrases, but I'm seeing many values of our own website url for "Original Search Engine". We do have a search bar on our site, could it be from this? Or is it actually from a search conducted outside of our own website, and is what originally landed them on our site?

Thanks,

Catherine