Deep links are used to give your inner pages link popularity. Building links to each of your websites category pages in a n effective method of link building for successful SEO. Deep linking is a powerful and effective way of link building.
URL Masking means that the visitors to the domain name will be forwarded to your destination website; however the URL in their browser address bar will remain the same. Also known as Stealth Redirection or URL Hiding, this will ensure that your visitors see the original domain name and not the destination URL.
Navigation means visitors would click other links which you have displayed in your menu or sidebar.
It is all a propos movement of your one page to different pages or post or categories within your sites.
Spider: A browser that downloads website pages.
Crawler: A programme that follow web pages automatically.
Basically, there is no difference between spiders and crawlers. the working of both are same although names are different. Spiders and Crawlers are exactly same. It's the one that crawl your site for indexing and ranking. It can also be called as bots.