SEO :- SEO is free service for getting traffic and generating backlink for website through Organic result. SEO stand search engine optimization.

SMO :- SMO is also free service but it is different to seo. SMO stand Social Media Optimization and it is process of getting more (bulk) traffic on your website and imporve your ROI.

PPC :- PPC (Pay Per Click) is similar to SEO but is paid marketing. When people with click on your ads it will diduct a some charge from it.