This could be anything it is their identification to google
google_ad_client = "pub-5038618221283072";
this is a bit more complicated, the height and width are from the format i don't think your meant to change them, however, there are some text only formats
i think the easiest way to show it is
<select id="text_img_format" name="format">
<optgroup label="Text and image ads:">
<option value="728x90"> 728 x 90 Leaderboard </option>
<option value="468x60"> 468 x 60 Banner </option>
<option value="300x250"> 300 x 250 Medium rectangle </option>
<option value="160x600"> 160 x 600 Wide Skyscraper </option>
<option value="120x600"> 120 x 600 Skyscraper </option> </optgroup>
<optgroup label="Text ads only:">
<option value="336x280"> 336 x 280 Large Rectangle </option>
<option value="250x250"> 250 x 250 Square </option>
<option value="234x60"> 234 x 60 Half Banner </option>
<option value="180x150"> 180 x 150 Small Rectangle </option>
<option value="125x125"> 125 x 125 Button </option>
<option value="120x240"> 120 x 240 Vertical Banner </option>
</optgroup>
</select>
they all have _as appended to their value and are google_ad_width x google_ad_height
google_ad_width = 728;
google_ad_height = 90;
google_ad_format = "728x90_as";
again could be anything they can setup channels to moniter ads on specific pages
either "text" "image" or "text_image" specifies the type of ads shown, text only, image only, both respectively
the colours for the ad
google_color_border = "FFFFFF";
google_color_bg = "FFFFFF";
google_color_link = "005CB1";
google_color_url = "005CB1";
google_color_text = "333333";
google_alternate_color = "FFFFFF";
there is another setting called link unit instead of ad unit but that gives no color settings and a different set of sizes, if you want i can tell you about that or it might be better as a different mod since its for putting links in blocks of text not in between text like this is a mod for i think
hope that helps