So many upholstery manufacturers are advertising that their frames now have mortise and tenon joinery. To really understand what they are actually referring to is first to really understand what a mortise and tenon joint is= I have provided that link to Wikipedia below.
Then contact any manufacturer and ask them to send you a photo of one of their mortise and tenon sofa or chair frames.
Then do a comparison of their photos to the images on Wikipedia. The difference will be startling, like comparing leather to vinyl.

Here is a link that might be useful: mortise and tenon info