A sub-domain is where your website does not have its own dedicated domain i.e. 'www.edzelwebdesign.com' . Instead, the web address, or url (Uniform Resource Locator) - would be something along the lines of 'www.edzelwebdesign.wix.com'.
What does this mean? Well, for one thing, you won't have to pay a penny for your website name or hosting costs (think of hosting costs as being the rent for your home on the web). But the downside is that your website won't be quite so easy to find on Google or other browsers if people are searching for it. I suppose it's a little bit like not having the post code, or having the kerbside address but not knowing which is your apartment number. You will need to send someone the exact url for them to be able to find it, instead of them typing 'edzelwebdesign' into Google and having it pop up on the first page - as it should with a named domain if your site manager has got the SEO -'Search Engine Optomisation'- right!
Sub-domains can be useful, though - if it's a hobby rather than a business, or you want to play around with design or content before committing to the ongoing costs of having your own domain then you can play around with a sub-domain, knowing that hardly anyone is going to notice what you're up to. I currently have two clients with sub-domains - you'll find them in my portfolio.
In our situation, if you commission a sub-domain website from me, all I will charge you for is my time, and perhaps an ongoing maintainence fee if you think you're likely to need amendments. (These can also be purchased on an 'ad-hoc' basis, too - but bear in mind that customers paying for regular maintainence will take precedence, so you may end up waiting a little while!)
Elaine, January 2021