Integrated Marketing is an approach to creating a unified and seamless experience for your customers, your donors, or your audience; a process designed to ensure that all messaging and communications strategies are consistent across all channels.
The goal of integrated marketing is that your business — or your organization, or who you are — is recognized and identified immediately; that there is cohesion across all of your marketing efforts.
Here is a terrific treatise on integrated marketing (from Hubspot). I'm not recommending you do your own marketing, but it's a good idea to understand this concept. Without it — well, you're just throwing darts in the dark.