With Gravity forms, an Anti-Spam feature can be enabled on the forms. To enable this feature:
  1. Navigate to Forms on the Dashboard
  2. Hover over the form in question and select Settings
  3. Click Form Settings
  4. Scroll to Form Options
  5. Mark the box for Enable anti-spam honeypot
  6. Click Update Form Settings
  7. Repeat for any other forms
This setting helps detect if the form is being filled out by a bot, instead of a real user. It will deter the submission if it picks up that a bot is filling out the form, as opposed to a real user. It won't keep a real person, who is trying to spam the site, from completing the form, but it can deter bot or automatic-type submissions.