How is SEO different from SEM and PPC?

SEM stands for search engine marketing – or, as it is more commonly known, search marketing.
Search marketing is a type of digital marketing. It is an umbrella term for the combination of SEO and PPC activities meant to drive traffic via organic search and paid search.
Put simply, search marketing is the process of gaining traffic and visibility from search engines through both paid and unpaid efforts.
So how do SEO and SEM differ? Technically they aren’t different – SEO is simply one-half of SEM:

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