An online audience is one you reach through online avenues besides direct email. As people use websites on the Internet, they leave a trail, and an online audience helps you track them on that trail. This trail consists of email addresses, website cookies, device IDs from computers, tablets, and cellphones, IP addresses assigned to those devices by website hosts and networks, and other activity tracking markers that websites (maybe even yours) collect as people shop, communicate, and browse online. Being able to follow that trail allows you to know where your prospects are so you can provide personalized touchpoints based on their online activity.