Tiny text is used sometimes to try and stuff keywords into a page. This is a spamming technique which is also referred to as "stuffing". Tiny text works by setting the font size smaller than normal size to try and cram (or stuff) as many keywords onto a page as possible. You can see an example of tiny text here.
Most search engines now will penalise if not ban sites using this technique. The way it works is to set your font size smaller than normal. In HTML language the font tag looks like this:
<font> and </font>
There are many different variables you can set with the <font> tag. Look below for some examples:
Green color
The tag for the above font is: <font color="green">Green color</font>
Blue color, size 4
The tag for the above font is: <font color="blue" size="4">Blue color, size 4</font>
Blue color, size 6
The tag for the above font is: <font color="blue" size="6">Blue color, size 6</font>
You can also change the type of font printed. For example:
Blue color, face arial
The tag for the above font is: <font color="blue" face="arial">Blue color, face arial</font>
This then leads us to the tiny text. As you can see from the above examples it is quite easy for people to manipulate text on their page. Below is tiny text which I have set as <font size="1">:
Tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text, tiny text.
All a search engine spider has to do is scan through the code of a page then look for <font size="1">. If a spider finds this in a page, it will most likely put a flag against that page or website and mark it as spam. How each engine reacts to this technique differs, however it would not be a good idea to use this technique as it is very easy to police by the search engines.