Within Textizen, your Campaigns represent overarching efforts. Each Campaign contains Polls, Messages, Groups, and Participants specific to that campaign. For example, the campaign "Riverfront Improvement Project" might be a Campaign, containing multiple polls and follow-up messages.
There is no limit to the number of Campaigns that you can have within your Organization. Just be sure to keep an eye on account limits so you don't exceed the maximum number of polls and survey responses. See Organization: Overview for how to check your account limits.