Slang. Jargon. Colloquial language. Patois...
If you have done your research and are knowledgeable about your niche, then you should have, at the very least, a basic understanding of the correct type of language to use in your website. Another word for this is 'jargon' which means the language or vocabulary specific to a trade or profession. Some niches have a language so specific, that people who are not 'in the know' would barely understand what the 'nichees' are talking about. (Excuse the made-up word - it just seemed to work.)
So should you use it?
Most definitely!
Let's look at an example:
Say you decide to create a website that sells surfboards. You are probably a surfer or hopefully, very interested in surfing. You understand surfers. You know where they 'hang out' (beaches), what they do for fun (surf), how they think (are there any waves today?) etc.
You understand your audience! (See Page 2)
And you already know how to talk to them because you ARE one of them!
Using jargon and slang in your webpages makes perfect sense
When you are creating your pages and posts within your SURFING website, you are no doubt going to be using words like aerial, air, barrel, 360, boardies, and face. You would be talking about surfing moves, (not flight paths or the atmosphere), a type of wave, (not a container for beer or oil), another surfing move (not a mathematics equation) etc.
You show your surfing customers the courtesy of speaking their language. English, for sure. But it's 'Surfing English' and it's a whole lot different to the English that gardeners or gamers or glamazons use!
It's all a part of being courteous to your customers so they become more than just passing visitors to your site. You are speaking their language, about their field of interest...so it won't be long before they see you as the 'Go-to' person, the guy with the knowledge, the gal with the smarts...an EXPERT who can be trusted. You will be turning visitors into customers and customers into raving fans.
And guess where the repeat sales come from? Those raving fans.
Excellent tutorial! Your conversational style creates a very friendly atmosphere for learning a difficult subject. I think you will reach those who desperately need this training in order to produce coherent content for their websites.
Cheers to you from the other Ellie!