Search Engine Optimization. It sounds big and complicated and an awful lot of bother when all you really want to do is make and sell your art or jewellery, scarves or toys or cards! But, there is lots of information available on the site to help make SEO work for you.
If you really want to dig into it, there is a substantial (25-page PDF) file Etsy Guide to SEO that you can download.
However, if you want the short course, and some step-by-step practical changes you can make today, head to this article How do I improve my shop's Search Engine Optimization? in the Help section. After making some important points about having a great product, and using your tags to best advantage, it moves on to some of the highlights of SEO. There are rules for how many characters will appear from your Shop Title and Item Titles, and it spells out what elements work for you from your Shop Sections and item descriptions too.
Image from sudlow, thanks!