When editing your Activity, you'll see a "Visibility" module in the top right corner with a few checkbox options.
The first option is to feature your event on your Homepage Slider. For more on how this works - Featuring Content On The Homepage.
The other checkbox gives you the option to hide an Activity from your public website. Typically this option is used for internally tracking activities such as newsletters, chapter meetings, etc. Things that your group would like to keep a record of, but don't want to publicize.
Checking this option for an Activity means it will not show up in the Homepage Slider, Recent Activities, Upcoming Activities or any other public list of your group's Activities.