SEO is an organic way of optimizing for search engines while SEM is not that different to SEO it is just that it involves paid advertising program for fast and better results.
SEM stands for Search Engine Marketing. It is the techniques of getting traffic or visibility on search engine. It is a part of internet marketing.Pay per Click and Cost Per Click are part of Search engine marketing.
These are several tools for SEM
Google AdWords Keyword Tool
SEO Book Keyword Tool
Google Traffic Estimator
Microsoft Ad Intelligence
SEO:
SEO is simply to make the site better for search engine in order to increase its visibility on the ..In the process of SEO you tend to rank your keywords on search results so that you’ll get traffic via search engine which is called organic traffic.
seo-It used to improves the visibility of the website and making website or webpage search engine friendly.
smo-It creates and increases the awareness of the product ,brand or event.
SEO: In layman's terms, improving your rank in search engine result listings on Google, Yahoo, Dogpile, etc.
SEM: The easiest distinction between SEO and SEM is if that the place the link shown is paid for, it's SEM.
In SEO you just only gain rank of your website on search engines and it is long process on the other hand in SEM you paid for every visit on your website and this technique pull your site top of the search engine search results in few time.
SEO stands for search engine optimization,it means to rank your website with specific keywords at top of Google.
SEM- Stands for Search Engine Marketing , it is a paid process which brings instant traffic to your website.