At the bottom of the page, where it says who's online, what does it mean by 'spiders'?

They are search engine bots.

Here's a definition from the internet:
A spider is a program that visits Web sites and reads their pages and other information in order to create entries for a search engine index. The major search engines on the Web all have such a program, which is also known as a "crawler" or a "bot."
If you check on "Who's Online" you'll see that the spiders that go through GB are Google, Bing, Yahoo, etc...

Ah thank you! I was thinking they were bad but if the allow search engines to help people find you then they're good ... ? I was more concerned that GB had an infestation of some kind.

Thanks Paul for the concern.

I didn't know what spiders are either MaG. Thanks for the explanation.

I was not even aware of that.... lol I thought creepy crawly spiders Duh1.....Thank You for that info PAul and Mag