Title is the heading of the webpage. The sentence or string enclosed between html title tag () is the title of your website. Search engines searches for the title of your website and displays title along with your website address on search result. Title is the most important element for both SEO and social sharing. Title should be less than 50 to 60 characters because search engine typically displays this length of string or sentence on search result. A good title can consist the primary keyword, secondary keyword and brand name. For example a fictitious gaming information providing sites title may be like "the future of gaming information is here". A webpage title should contain a proper glimpse of the website. title is important element as an identification of your website for user experience, SEO and social sharing. So have a nice and catching title.
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Description is the full interpretation of your website content and features. Most often it is a short paragraph that describe what are features and information provided by the website to its visitors. You may consider it a advertising of your website. Although not important for search engine ranking but very important for hits or visits through search engine results. Description should be less than 150 character because search engine shows this length of paragraph on search result. And every page of website should contain an unique description to avoid description duplication. Description is the definition of your website for user experience so form it as complete but short and precise illustration of your website.

Meta keywords are keywords inside Meta tags. Meta keywords are not likely to be used for search engine ranking. the words of title and description can be used as meta keywords. it is a good idea for SEO other than search engine ranking.

Keyword usage is the using of your keywords inside Meta tags and contents of your website. Use keywords that describes your site properly for precise search engine result of your website.

Sitemap is a xml file which contain full list of your website urls. It is used to include directories of your websites for crawling and indexing for search engine and access for users. it can help search engine robots for indexing your website more fast and deeply. It is roughly an opposite of robots.txt You can create a sitemap.xml by various free and paid service or you can write it with proper way (read about how write a sitemap).

Also keep these things in mind:
1) Sitemap must be less than 10 MB (10,485,760 bytes) and can contain maximum 50,000 urls. if you have more uls than this create multiple sitemap files and use a sitemap index file.
2) Put your sitemap in website root directory and add the url of your sitemap in robots.txt.
3) sitemap.xml can be compressed using grip for faster loading.

Broken link: a broken link is an inaccessible link or url of a website. a higher rate of broken links have a negative effect on search engine ranking due to reduced link equity. it also has a bad impact on user experience. There are several reasons for broken link. All are listed below.
1) An incorrect link entered by you.
2) The destination website removed the linked web page given by you. (A common 404 error).
3) The destination website is irreversibly moved or not exists anymore. (Changing domain or site blocked or dysfunctional).
4) User may behind some firewall or alike software or security mechanism that is blocking the access to the destination website.
5) You have provided a link to a site that is blocked by firewall or alike software for outside access.
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GZIP is a generic compressor that can be applied to any stream of bytes: under the hood it remembers some of the previously seen content and attempts to find and replace duplicate data fragments in an efficient way - for the curious, great low-level explanation of GZIP. However, in practice, GZIP performs best on text-based content, often achieving compression rates of as high as 70-90% for larger files, whereas running GZIP on assets that are already compressed via alternative algorithms (e.g. most image formats) yields little to no improvement. It is also recommended that, GZIP compressed size should be <=33 KB

Inline css is the css code reside in html page under html tags not in external .css file. Inline css increases the loading time of your webpage which is an important search engine ranking factor. So try not to use inline css.

Micro data is the information underlying a html string or paragraph. Consider a string “Avatar”, it could refer a profile picture on forum, blog or social networking site or may it refer to a highly successful 3D movie. Microdot is used to specify the reference or underlying information about an html string. Microdata gives chances to search engine and other application for better understanding of your content and better display significantly on search result.
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If multiple domain name is registered under single ip address the search bots can label other sites as duplicates of one sites. This is ip canonicalization. Little bit like url canonicalizaion. To solve this use redirects.
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