What is the difference between a Search Engine and a Search Directory?

Search Engine Web Directory
It uses programs like robots,crawlers or spiders which gives the results for your searches. It is human powered, Site owners submit their sites to directories and determine which site to be include in directory.
Search engines don't have any category specific page.

Search directories have different specified categories where users can search URLs and links.

Examples: Google, Bing, Yahoo, Ask.com, Baidu, AOl.com, DuckDuckGo, Wolframalpha etc. Examples: dmoz.org, ii.org , business.com, botw.org,sunsteam.com etc.