What is <base href="http://www.xxx.com/" /> ?

[Mean]

It is in my showthread page, under meta tags.

<base href="http://www.xxx.com/" />

I dont know what it is.
My question is, is that helps meta tags or is it not very important ?
And what is this for ?

[Pc 1203]

I believe it means that all links on that page will start with a:

http://www.xxx.com

- Pc1203

[Mean]

Thanks. But is that helps meta tags for Search ENgine Optimization ??

[Dismounted]

The base tag isn't a meta tag...