What do you know about SEM.?

Can anyone tell me about social Signals and how it is useful?

Can anyone tell me what is a effect of SMO

Can anyone tell me about google adwords planner.?

What are backlinks ?

What is Google Crawling ?

What is Web 2.0 ?

Please tell me which SEO factors can not in our control?

What is the difference between a do-follow and no-follow and how are they used?

Please describe the relationship between SEO and SEM?