SEM is a broader term than SEO, and is used to encompass different options available to use a search engine’s technology, including paid ads. SEM is often used to describe acts associated with researching, submitting and positioning a website within search engines.  It includes things such as search engine optimization, paid listings and other search-engine related services and functions that will increase exposure and traffic to your Web site. 
Search engine optimization is a method for sustainably influences search engine rankings. Google and other search engines calculate their search results for keywords using highly complex algorithms. The individual ranking factors and their weighting within the ranking calculation are well-guarded intellectual property that belongs to the search engines and is not publicly disclosed.
When it comes to search engine marketing, there may be no larger misnomer, no more archaic term than the ubiquitous keyword. In my view, there should be an official migration to the more accurate term keyphrase, but for now I will be forced to use what I consider to be an inaccurate term. My frustration with this term is that it quite simply implies a single word, which is rarely the strategy that we employ when doing keyword research and selection in the service of PPC and SEO campaigns.

For instance, you might use Facebook’s Lookalike Audiences to get your message in front of an audience similar to your core demographic. Or, you could pay a social media influencer to share images of your products to her already well-established community. Paid social media can attract new customers to your brand or product, but you’ll want to conduct market research and A/B testing before investing too much in one social media channel.
Creating the link between SEO and PPC represents an integral part of the SEM concept. Sometimes, especially when separate teams work on SEO and PPC and the efforts are not synced, positive results of aligning their strategies can be lost. The aim of both SEO and PPC is maximizing the visibility in search and thus, their actions to achieve it should be centrally coordinated. Both teams can benefit from setting shared goals and combined metrics, evaluating data together to determine future strategy or discuss which of the tools works better to get the traffic for selected keywords in the national and local search results. Thanks to this, the search visibility can be increased along with optimizing both conversions and costs.[22]
– Collect conversion related data from your PPC campaign and use it to convert your organic search visitors better. Also, keywords that worked for you in PPC are best to optimize your website for, so using them for SEO purposes makes sense. Your PPC campaign will end, but the rankings you achieve for the same keyword will remain for quite some time.

Because someone who is looking for something that specific is probably a much more qualified searcher for your product or service (presuming you're in the blogging space) than someone looking for something really generic. And because long-tail keywords tend to be more specific, it's usually easier to tell what people who search for those keywords are really looking for. Someone searching for the head term "blogging," on the other hand, could be searching it for a whole host of reasons unrelated to your business.
Optimization techniques are highly tuned to the dominant search engines in the target market. The search engines' market shares vary from market to market, as does competition. In 2003, Danny Sullivan stated that Google represented about 75% of all searches.[64] In markets outside the United States, Google's share is often larger, and Google remains the dominant search engine worldwide as of 2007.[65] As of 2006, Google had an 85–90% market share in Germany.[66] While there were hundreds of SEO firms in the US at that time, there were only about five in Germany.[66] As of June 2008, the market share of Google in the UK was close to 90% according to Hitwise.[67] That market share is achieved in a number of countries.
Paid channel marketing is something you’ve probably come across in some form or another. Other names for this topic include Search Engine Marketing (SEM), online advertising, or pay-per-click (PPC) marketing. Very often, marketers use these terms interchangeably to describe the same concept — traffic purchased through online ads. Marketers frequently shy away from this technique because it costs money. This perspective will put you at a significant disadvantage. It’s not uncommon for companies to run PPC campaigns with uncapped budgets. Why? Because you should be generating an ROI anyway. This post walks through the basics of how. Get Started
Search engine optimization is a method for sustainably influences search engine rankings. Google and other search engines calculate their search results for keywords using highly complex algorithms. The individual ranking factors and their weighting within the ranking calculation are well-guarded intellectual property that belongs to the search engines and is not publicly disclosed.
Some search engines have also reached out to the SEO industry, and are frequent sponsors and guests at SEO conferences, webchats, and seminars. Major search engines provide information and guidelines to help with website optimization.[18][19] Google has a Sitemaps program to help webmasters learn if Google is having any problems indexing their website and also provides data on Google traffic to the website.[20] Bing Webmaster Tools provides a way for webmasters to submit a sitemap and web feeds, allows users to determine the "crawl rate", and track the web pages index status.
I want you to do some SERP investigation, meaning perform a search query in Google, see what comes back to you, and then figure out from there what Google believes to be relevant to the keywords searches. What does Google think is the content that will answer this searcher's query? You're trying to figure out intent, the type of content that's required, and whatever missing pieces might be there. If you can find holes where, hey, no one is serving this, but I know that people want the answer to it, you might be able to fill that gap and take over that ranking position. Thanks to Gaetano, @gaetano_nyc, for the great suggestion on this one.
Be sure to re-evaluate these keywords every few months -- once a quarter is a good benchmark, but some businesses like to do it even more often than that. As you gain even more authority in the SERPs, you'll find that you can add more and more keywords to your lists to tackle as you work on maintaining your current presence, and then growing in new areas on top of that.
SEM is better for testing than SEO. Because you can immediately turn SEM paid ads off and on, it’s a great strategy for testing. You can quickly revise your ad copy, target new audiences, and change landing page content to test your new tactics. This flexibility allows you to see differences in your strategies immediately. You cannot accomplish this through SEO, as it would take too much time to make changes and monitor differences in results.
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