Early web designers always had a clear/empty image file in the graphics folder of their projects. Usually it would be called clear.gif. Mine was — 0.gif. And most commonly it would be just 1 pixel of nothing. The one on Geocities is 10×10 pixels.
Clear gifs were irreplaceable in the world of pre-CSS layouts. Invisible and small graphics could be stretched in width and height, keeping visible elements of the page on desirable distance.
On the page where I found Geocities’ c.gif, it was used in a very clumsy way: 23 clear gifs in a table row to make an invisible line of 751 pixels. A human being wouldn’t do it. Yahoo! PageBuilder did.