A keyword is the word on your page related to the meaning or point of the article. Previously it was employed whereby careful repetition of this keyword throughout the page it would affect its ranking and importance. This technique is now pretty much obsolete due to Search Engines changing their methods of grading your pages.
* Note this misconception still exists even though the second article is dated 2005!
So what is important with keywords?
The need for keywords still exists but its application is different and has moved away from the complicated calculation of spreading keywords in specific parts of your information to make it more important or relevant in Search Engines eyes.
Now the keywords can and should be used in the proper manner of the subject, they can be highlighted with bold tags and the text size increased and also with the use of the tags called H1 H2 H3 etc. (H stands for Heading and the number dictates the importance of the title.) with the end aim of making the information easier for the visitor to read and enjoy.
By doing this it has allowed the information that appears online to be more natrual to read and indeed, enjoyable and interesting to visitors.