Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.
I use a lot of fly fishing, photography, and especially entomology jargon on this site. The site incorporates these definitions wherever they're used, but and this page lists together every single form of every term used on this site.
You can also click a link from one of the in-line definitions across the site to come to its full definition page, seeing sub-definitions used within it highlighted and illustrated.