Google’s ‘Ad Customisers’ in search ads work like the ‘keyword insertion’ feature, which puts the actual search term which called up the ad into your ad text. Ad customisers, however, can insert any type of text at all.
Using this feature, your ads are completed using data which you have uploaded to Google Ads in a spreadsheet file. You can control the text with information including keywords, ad groups, campaigns or locations, and create whole headlines and descriptions which can then be dynamically called into your ads when a targeting criteria is met. So, for example, an ad which meets a certain location criterion could be completely rewritten to make a special offer for that location, such as a shipping offer.