online

Simply put, yes social media marketing is different from other forms of marketing but at the same time, it is a component of digital marketing. When you discuss social media optimization, you focus only on Facebook, LinkedIn, Twitter, Pinterest, Instagram and other similar platforms. You discuss ways to optimize social media posts and videos. Also you consider advertising on social media platforms. But when you discuss online marketing you discuss all the components including search marketing, social media and paid ads.
Online marketing is a bigger concept and social media is a part of it. You can say that your focus in digital marketing is on social platforms. But saying that you are doing social media marketing and not online marketing would be wrong. It shows that you have little knowledge on digital media and its components. When you optimize your website for social media, you adopt different ways than search marketing.
People often segregate social media from online marketing due to their ignorance on digital marketing and also due to the individual nature of social media. Every social media profile is complete and independent from others. But in reality, it is a crucial element of digital marketing that is a bigger concept.