Is it purely the Title of the ad (with keywords) that triggers the ad to show? Or if an ad has keywords in the 2 description lines but not in the title, can that still trigger the ad? I know its suggested to have keywords in your title.
Neither. Your keywords trigger the ad to show - nothing in your ad triggers it. The reason to put keywords in the title, is because a) it increases relevancy and helps your Quality Score and b) the keyword is bolded in the results so is more eyecatching for the searcher and they are more likely to click on it.
So a searcher can type in a keyword phrase, the keyword is in your ad group as a match type that would allow it to trigger the ad, you have not put the keyword phrase in the title or description lines at all in the ad and it could still show? Im glad ive asked now because it shows how ive misunderstood what may trigger the ad.
In theory, if you are selling hair widgets, and you have keywords and phrases in your list like widgets hair widgets blue widgets widgets for sale You can have an ad that says something like Cheap Hair Accessories Best Prices and All Varieties Quick Delivery and Attentive Service ww.haird*s.co and it will be triggered by somebody searching for widgets. In practice people don't do that, because as I said, you'll probably end up paying more because it depresses your quality score, and with no keyword being bolded, it won't stand out as much as other ads and organic listings.
Thanks very much for explaining magda, i understand it much better now, i see what you mean too that its much better to include the keywords for relevancy, QS....