What is Ad Code in Google Adsense?

Ad code is a combination of HTML and Js code used for providing the ads on a page where we add the code.
The js part loads the SDK and functionality, while the HTML code marks place and dimension along with other details to render(draw and display) the ad on a page.

Ad code in Google AdSense is a snippet of HTML or JavaScript code that you can add to your website to display ads from the Google AdSense network. The code contains information about the ad format, such as the size and type of ad, as well as a unique publisher ID that identifies your website to the AdSense system. Once you have added the ad code to your website, Google AdSense will automatically serve relevant ads to your website, and you will earn money every time a user clicks on one of the ads. The AdSense program allows website owners and bloggers to display targeted ads on their websites and earn a percentage of the revenue when a user clicks on an ad.