For me; SEO is:
Cleanly coded website, minor file sizes for all images & responsive.
1. First off, making your website code immaculate so relevant search spiders can read it as quickly and efficiently as possible.
2.Make sure the site structure is well organized (all images have keyword specific file names, content to have keyword specific phrases in all h1 -h3, p, ). All .js and .css to be minimized. Have 2 to 3 good images in your content (keywords)
3. Be active on the web. Write blog/news posts every month related to your business/service/product industry. Have a G+ account.
4. Have a content marketing strategy