Keywords are the words that are used to reveal the internal structure of an author's reasoning. While they are used primarily for rhetoric, they are also used in a strictly grammatical sense for structural composition, reasoning, and comprehension. Indeed, they are an essential part of any language.

There are many different types of keyword categories including: Conclusion, Continuation, Contrast, Emphasis, Evidence, Illustration and Sequence. Each category serves its own function, as do the keywords inside of a given category.

Corpus Linguistic Key Words

In corpus linguistics, key words can be identified as words which appear with statistically unusual frequency in a text or a corpus of texts; as such they are identified by software by comparing a word-list of the text in question with a word-list based on a larger reference corpus. This procedure is used for example by WordSmith.

Meta keywords

On the web, a keyword is a reference to the content and/or the type of meta element included in a given web page's HTML code to aid in the page's indexing. A keyword meta element may include several comma-separated keywords (or keyword phrases, each of which may contain several individual words) as follows :

Looking back to the 90s, the search engine crawlers were relatively poor in terms of analysis capabilities, and, thus, the meta keywords were a simple way to detect the topics of a page. Historically, it has been the first way to optimize for search engines, however, no major search engine today claims to read the keywords which has raised the question of whether they are still needed at all.

Query terms

The term "keyword" also refers to the terms or phrases submitted by a user of a search engine. For example, a search of the phrase "keyword search" via the Google search engine reveals a set of search engine results that relate to the specified topic "keyword search". The link with the meta keywords previously defined was real in the last century, however, the search engines are actually using much more advanced techniques (statistics, natural language processing, web topology...) to enhance their results and thus the decreasing relation between those two type of keywords.

But a technical definition of "keyword" does not provide insight to their significance or how to work with them successfully. Significance is straightforward: as more and more of human knowledge is digitized and therefore 'searchable,' the ability to understand and successfully develop, organize and manipulate keywords leads directly to access to critically important information, and gets information to the right audience.

Working with keywords

There are two aspects to working with keywords: from the perspective of the information provider, and from the perspective of the information users (i.e. "producers" and "users").

Information producers: For information publishers (meaning anyone providing digitally searchable content they want to be found by a given audience), there are a tremendous number of subtleties to developing a keyword framework that a) adequately describes the content, and b) connects that content to the right audience. The first mistake many publishers make is to 'underdescribe' their content by using a keyword that is too general to be useful. For example, to say the keyword for this essay is "keywords" would be such an 'underdescription' -- a better keyword (really, keyword phrase) would be something like "keyword development" or "keyword definition" or "how keywords are used." The second mistake publishers frequently make is to not put themselves in the mind of the searcher, but to instead use keywords that are relevant to them. The easy fix for this lack of perspective is simply to do the footwork: make a list of keywords that might be relevant and then verify whether or not they garner searches by checking the list on a database that collects such information and provides "suggestions" that you may never thought of (Keyword Discovery, Wordtracker and Overture are just three such services). Never make assumptions -- for example, according to one of the keyword databases listed, "keyword assistance" gets zero searches per year but "keyword research" gets 50 searches per year. that a very common error is the "verify" a keyword by typing it into a search engine and seeing how many web pages come back. This indicates is how many pages have that keyword in their content, not how many people are searching for that keyword, and there is no relationship between those two datum. It is important to keep in mind the need to be flexible -- there are as many ways to describe something (and develop a search query for it) as there are people with keyboards -- but not too flexible. The goal is precision, and the searcher will appreciate efforts to describe precisely what your content is about if it is precisely what they are looking for.