# What is a pickup ion?

I've been reading several publications about Titan's atmosphere and chemistry, and the term "pickup ion" kept appearing here and there (see this publication for example).
I looked it up and found the Wikipedia entry, but could not understand the essence of the term (only later I noticed that apparently even Wikipedia is not entirely satisfied with this entry, since it is regarded as "too technical for most readers to understand.").

Other Google results just give other publications where the term is used, but I could not find any definition there too. I also could not find any questions about it here.

So if anyone could provide a concise and clear explanation, I'd be grateful. I am a 1st-year chemistry M.Sc. student, so you can adjust the explanations accordingly.