If your account was migrated from Google Apps, the migration process included everything Google had saved in your Contacts, including not only Contacts you added yourself, but also "Other Contacts" which is a collection of every email address that has ever emailed you or you have emailed, without your even having saved the contact information.

One easy way to manage all of your contacts in our system, is to create a new view or edit the Default View to only show contacts that have a First Name, Last Name, or Organization.

For instance, in this example, a filter is set on the Default View to filter contacts where the First Name field "is not blank".