SEO is search engine optimization.
Any one who
a. builds a public web site and
b. wants it higher up in search results (in Google, Bing, Yahoo, etc)
goes through SEO exercise.
Same applies for your resume.
When you start your job search, you post your resume in a job board (Dice, Monster, etc).
Every job board uses a private search engine, to make sure recruiters can see your profile in search results.
Every search implementation has its individual features and quirks. But on a basic level, they all work in the same fashion.
SEO is about improving the ranking. If your resume shows up in the 23rd page of search result, nobody is looking at it.
To SEO you resume:
1. Make sure your resume has all the keywords that sufficiently describe your core skills. Add the right phrases that use the keywords. Add version information to all the skills. You can use a tool like this to automatically get the keywords from your resume. Use its results across all job boards.
2. Make sure it has all the related keywords. These are keywords that often appear in the context of your primary keywords. For instance, 'SE38' is primary keyword. "Debugger" is a related keyword.
3. Try not to cheat the search engines into boosting your resume. They are every bit tuned to find the right document. So your best bet is to organically grow your resume.Make sure it has sufficient occurrence of the primary skills. Less the number of occurrences, farther you are from the first page.
4. Maintain two versions: i.Searchable resume ii. Readable resume. More on this later.
5. Gather 20 job requirements that best fit your skills. Make sure your resume has all the keywords in the requirements.