Targeted ads present you with advertising keyed to your interests and history. If you're an Amazon customer, you've likely received emails related to your recent browsing choices. Gmail ads are based on your Google account contents. Apple is no different. iAds tracks you and offers ads that best match your profile.
Apple offers an opt-out choice if you'd rather be served random ads from their iAds service. To use it, first visit http://oo.apple.com from your device. Then set the switch from ON to OFF. You'll be asked to confirm. Tap the red "Opt Out" button.
When disabled, you'll still see iAds. However, these will not be tied to you or your specific interests in any way.
If at some time you feel the need to return to the previous state of things, you can always revisit the Opt Out page and update your settings.