Search Engine: A machine "tuned" by humans to index web pages. For instance, Excite.
Algorithm: The way in which search engine is "tuned". An algorithm is way search engine will determine ranks - it is way search engine is programmed to determine ranks. An algorithm may take only certain things into account - like keywords in title or link popularity. Some engines use cyclical algorithms - meaning they may change algorithms from week to week.
Directory: A list of sites compiled by humans. For instance, Yahoo!
Spider: A spider goes to your site and finds your pages. It then stores those pages in a database for future retrieval by search engine.
Indexing: When search engine takes pages from database that spider has created and places them in an order based on algorithms of that engine. All search engines have a different indexing process - due to different algorithms - that's why you get different results in different engines.
Query: The keywords that a person types into a search box. A person is "querying" search engine.
Crawling: When spider follows links from page you submit - spider is "crawling" your site.
Automatic Update: When spider returns to your pages at periodic intervals to check to see if you've made any changes.
Optimizing: You can optimize, tune or configure your web pages for a specific search engine. This means that you are employing specific strategies for specific engines.
Spam: - Using same keyword more than three times in your keywords tag.
- Putting keywords into your tags that has nothing to do with your actual page content.
- Using text, spacers, or borders same color as background.
- Using tiny text with keywords in an attempt to increase ranks.
B. Search Engines v. Directories
There is a difference between a search engine and a directory. A search engine is a machine - or a "robot". A human may program algorithms for a search engine, but a human will have nothing to do with your site when spider is visiting your site or engine is indexing your pages.
A directory can be compiled by a robot, but more often than not, it is compiled by humans. Yahoo! is a prime example of a directory. When you submit your site to Yahoo! a human will review your site for consideration in their index.
The lines between search engines and directories are becoming jaded. This is because each major "search engine" is associated with a "directory." For instance, we used to call AltaVista a search engine. However, we have to be careful with that terminology. When you go to AltaVista and you type in a search - you are definitely getting results from "engine" part of AltaVista. But when you search down through "categories" - you haven't typed anything into "search box" - you are now getting results from a directory (these results come from two directories - Open Directory Project and LookSmart.)