An important focus word or phrases related to your business, that best describes your business and is likely to be hit by many. 

LSI keywords – Latest Semantic Indexing keywords are related keywords to the seed keyword.
Not exactly being the synonyms, these keywords are particularly linked to the product or
the service.
Eg: Seed Keyword – Digital Marketing, LSI keywords – SEO, SMO, content marketing etc.

Long Tail Keywords – These are long phrase keywords derived from the seed keyword itself.
Having low search volume and less competition, they have better conversion rate.
Eg: Seed Keyword : Digital Marketing, Long tail keyword: Best digital marketing services, digital marketing services in Delhi, digital marketing for small businesses