In Latin, the word corona means crown. Here's a handy-dandy clip art of a crown.
In poetry and thus in music, a corona is when the last line of a poem is the first line of the following poem. What the heck does this have to do with country music, you ask? Consider Brad Paisley. I remember listening to his first two albums over and over and over again. Okay, I confess it, I do not own every Brad Paisley album. I only own the first three. I noticed back then that the songs would lead into one another - the way real albums do. You know that Brad Paisley really loves the music he makes and really cares about its presentation because he makes an album, not just individual songs thrown together. Now, I haven't bought a Brad Paisley album in years, I noticed while listening to Pandora that Brad Paisley is still up to his old corona-type tricks. The radio stations cut the songs off early or talk over the endings (so obnoxious), but Pandora kindly just plays the whole song beginning to end. The song "Old Alabama" from the most recent BP album, This is Country Music, ends with a piece of the song "This is Country Music."
A circlet is just what it sounds like, a little circle, often what you would picture to be on the head of a young prince or princess, yes? In other words, it works as a small crown.
I choose circlet as the description of a song that begins and ends with the same line. I like circlet because it is similar to a corona, but smaller/more confined. Also, I prefer the image of a circlet over the image of a crown because our culture, when we picture a crown, we picture something like the above, though perhaps more be-jeweled. You do not picture what makes it a crown - the circle-ness. But when you picture a circlet, you see the circle, so the image fits the definition.
Numerous songs jump to mind when you think of what a circlet must be, do they not? The first one to come to my mind is Tim McGraw's "Don't Take the Girl" which opens and closes with the line "Johnny's daddy was takin' him fishin' / when he was eight years old."
More recently, Jake Owen's song "Alone with You" is a circlet. It begins and ends with the line "I don't see you laugh / you don't call me back, / but you kiss me when you're drunk."
Why is it cool to know this kind of stuff? Easy, you love your music, but you want to love it more. The more you understand the techniques employed by musicians and vocalists, the more fully you can enjoy the song.