Some definitions and helpful links

Definitions

Spiders
A Web crawler (also known as a Web spider or Web robot) is a program or automated script which browses the World Wide Web in a methodical, automated manner.

Keywords
A keyword in an internet search is one of the words used to find matching pages. It was popularized during the early days of internet search as it was not possible to ask plaintext questions and find the desired sites. Searches gave the best results if only a few key words were chosen and searched for. These “keywords” captured the essence of the topic in question and were likely to be on all sites containing relevant information.

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. Paid inclusion products are provided by most search engine companies, the most notable exception being Google.

Paid Placement (also known as pay-per-click))
Paid inclusion is a search engine marketing product where the search engine company charges fees related to inclusion of websites in their search index. Paid inclusion products are provided by most search engine companies, the most notable exception being Google.