Digital Marketing is the use of digital channels to promote products and services. These channels can include the internet, social media, digital signage, telephony, e-books, games, and other forms of digital content. Tactics utilized on these channels can include SEO (search engine optimization), SEM (search engine marketing), and link building.
So Content Marketing without a solid Digital Marketing plan is like creating a spectacular birthday cake without sending out any invitations to the party. Maybe someone will randomly drop by and give it a try, but odds are better that you'll end up sitting there with it all alone.
Likewise, a Digital Marketing strategy with no great Content Marketing plan is like a brand new, four lane highway that leads anywhere you want to go, with a smooth ride for miles ahead. But, after taking stock of your transportation, you find the only vehicle you have to trek on is a three-wheeled skateboard. You'll get no distance at all, despite the opportunity.
Both of these marketing categories make up what is known as Inbound Marketing. This simply means customers or prospects opt-in to these efforts, through methods including sign-ups, social media, making calls to your company or giving permission for you to call them, and links found in search engines. This is opposed to the interrupt provided by Outbound, or Traditional Marketing tactics like television and radio commercials, cold calls, print ads, mailers, e-blasts and trade show appearances.