The Activity tab in a profile is a collection of online and offline data points that you're having with your audience. Data points include email sends, donations, form fills, page views etc. You can segment down on any interaction data points you have within your account.
You can segment on any Activity through Audience > Activity and drill down further by specific action such as a phone bank and even more granular by applying time stamps.
Below is just a snippet of the information Crowdskout is collecting both on and offline that lives within a profile.