Gated content is online materials, such as white papers, articles and videos, that require that users fill out a form before they can access them. The form may just ask for the user's name and email address or might demand more details, typically about their jobs and organizations. The form pages are sometimes referred to as information gates or registration walls.
Ungated content, on the other hand, is presented to the user upon request. There may be some option to sign up or provide data for an incentive -- typically more content or a newsletter -- but the user can access the data without providing any information.
The purpose of gated content is lead generation: acquiring user information for potential leads or prospects. However, because Google doesn't crawl content that's behind a wall, fewer people will find the content in the first place. According to content marketing expert David Meerman Scott, ungated content is downloaded 20 to 50 times more often than gated content. Scott makes his own content freely available and ungated and suggests that marketers either follow suit or at least reduce the number of fields in the forms presented to users.
Chris Keller on using non-gated content to increase high-quality leads: