Social media marketing is any sort of activity your business takes on social media that is unpaid or organic in nature. In other words, posting and engaging. Basically anything that doesn’t require you to pay the social media company to reach your target audience. This can include posting content on your channels, answering messages, liking or commenting on posts.
On the other hand, social media advertising is any form of social media activity that is paid, like boosting posts throughout a social network or running a targeted campaign at a specific audience (eg. location, household income, hobbies, etc.). You are paying to get more visibility or to get in front of users who may not be following your brand. And paying for the privilege of making use of the information that social media companies gather about their users.