The internet has a long memory, and that can make attempting to learn about technical issues, especially quickly moving ones, a trying experience. One thing to keep in mind when you're trying to learn about Search Engine Optimization (SEO) is that when articles just refer to "keywords" they probably aren't referring to the Meta Keywords tag. When an SEO article talks about "keywords" they're referring to the search words that you're trying to gear that page around. So if you said "I want my company to rank higher for the search 'widget suppliers in Iowa'" those would be your keywords, or your key phrase.
The Meta Keywords tag is a remnant of a bygone era of the internet when search engines lacked the intelligence and the power to try and figure out for themselves what the page they're indexing is about. They look something like this:
<META NAME="KEYWORDS" CONTENT="list of terms, each separated, by a comma">
These tags are virtually ignored by every search engine of any consequence. You might find an occasional, recently written, article that tries to convince people that the tag isn't dead, it's just mostly dead. You'll also read lots of opinions how even if it carries no weight, "it can't hurt, so why not."
The main reason? Because it can hurt. The problem with the format of the META Keywords tag is it practically begs to be a dumping ground of every possible combination of words and phrases that may or may not pertain to a specific page. Google, and other search engines, don't like to be played. One of the things they look for is keyword stuffing, which basically means certain words are used way too often to be "real" or natural. While search engines put almost no stock into the words in the META Keywords as far as helping you rank higher, it's a fair bet a repetitive and overdone META Keywords tag is one of the first red flags for people trying to play games.
Furthermore, even if you play it safe with the META Keywords tag, it doesn't help enough to be worth your time. Spending that time on intelligently, and naturally, working your keywords into the content on that page will pay much bigger dividends, especially since anyone that would happen upon that page will be looking for those words and phrases as well.
A good rule of thumb, if you aren't ready to give up the META Keywords tag, is to pretend you were showing that content to your users. An even better rule of thumb is to actually show that content to your users. Put something on the bottom of the page like:
Related Terms: META Keywords tag, SEO, Search Engine Optimization, etc.
Then, only put things in the META Keywords tag that you're willing to put on the page. It's a good way to keep the list "honest", short, and safe, because chances are you aren't going to show your users a massive, repetitive list. Most importantly, that list of words is then part of the content of the page, which will do you way more good than putting those same words in the keywords tag will.