Some of the major free webspace providers have started to add pop-up ads to users homepages. "Popup" ads are very irritating. You should try to avoid pop-up ads on your page, since it will distract your visitors. It is also very likely that most of "your" visitors will only see the pop-up ad and click on it. In other words, they will miss your site.

Some providers will let you deside if you want a pop-up ad or an adbanner (for instance Geocities and Hypermart). If they allow you to choose this, it is indicated here as "Popup/Banner".

"Adframe" means that the free host will insert a frame at the top of your site and a banner will appear in this frame.

"Watermark" is a new form of logo ad displayed usually at the corner of the screen. Geocities was the first to use this form of ad. It's not visible in older browsers (version 3.x and older).

"Textlink" means that they will insert a text ad on your pages.

And finally "No ads" means that they claim that they will not put ads on users pages. Remember that most will end up doing so anyway later, since they have to earn money somehow...

Since each free host have their own definitions, you need to take a look at their Help pages or FAQ pages to find out the exact details of the type of ad they will put on your site.