The practice of marketing , advertising & Optimizing a website in search engines is referred to search Engine Marketing.

SEM methods include

Search Engine Optimization (or SEO)
Paid Placement
Paid Inclusion

Search Engine Optimization

It is process of improving quality traffic to a web site from search engines organic search results.

Search engine’s don’t see pages the same way we doe, there’s no color, no flash, that makes them go “this is a professional page” – you have to make it know what the page is about, and SEO makes sure the search engine sees your page the same way you do

Paid Placement(PPC)

It is an advertising model used on search engines, advertising networks, and content websites, where advertisers only pay when a user actually clicks on an ad to visit the advertiser's website. Advertisers bid on keywords they believe their target market would type in the search bar when they are looking for a product or service.

Paid Inclusion

Paid inclusion is a search engine marketing product where the search engine company charges fees related to inclusion of websites in their search index.