If F3 finds the next item, what finds the previous one?

Once you've started a search in, say, the Registry, F3 will find the next entry, and the next, and so on.

But is there such a hotkey to back up to the previous one?

That's totally program-specific. F3 does that for the built-in registry editor, but other tools could have different ones. By no means there is a standard. F3 happens to be a common choice for that, but many programs use other means.

"Find previous" function is even more obscure. For instance, in the registry editor it doesn't even exists, much less in hotkey form. Other software could implement it and even give some shortcut for it.

Bottom line, look in each program what does it do. There is no ubiquitious hotkey like CTRL+C or CTRL+V for copy and paste.

I was only using the Registry as an example of an area where F3 finds the next listing.

But if you say there's no such thing as a 'reverse F3', I'll take your word for it

gladson1976, thanks