A chorus is a bunch of people who sings together, right? A refrain is a segment of words (or maybe non-words) that is repeated.
Some different pop-rock-blues-hip-hop-soul-jazz chorus types that come to mind are three:
- A repeated phrase like, "You can't always get what you want" or "The answer, my friend is blowing in the wind".
- A few lines almost a mini-verse like, "Cash rules everything around me, C.R.E.A.M. Get the money, dollar dollar bill, y'all" or "This is a man's world, this is a man's world, But it wouldn't be nothing, nothing without a woman or a girl"
- A culmination of the verse like Hank Williams' "Another man on the lost highway" or Johnny Cash's "Cry, cry, cry".
When we get inspired–hit/blessed with some inspiration, it may not be a whole song, eh? It might be a first line or more of something that would be a verse.
A song that comes to mind is Everybody Knows by Leonard Cohen
Everybody knows that the dice are loaded
Everybody rolls with their fingers crossed
Everybody knows the war is over
Everybody knows the good guys lost
Everybody knows the fight was fixed
The poor stay poor, the rich get rich
That's how it goes
Everybody knows
Leonard talks about spending years on his songs. This one? A classic. Maybe not Halleluja, but fun. I can think of three other "Everybody Knows" songs off hand (MC Trachiotomy, Tiana Hux, Mad haPPy) and there are probably literally hundreds. What came first to Leonard? Was the songs first line or two the first idea he had?
I guarantee–at least I think I guarantee–that he didn't sit down and think, "I want to write a song about stuff that everybody knows." Everybody knows is basically filler. It's a frame for the actual content. A framework, a structure. Maybe he wanted to write a song about how we're fucked and we all know it and don't change it.
Maybe this was the first line that came to him
Everybody knows that you've been faithful
Ah, give or take a night or two
Raunchy verse:
Everybody knows that you love me baby
Everybody knows that you really do
Everybody knows that you've been faithful
Ah, give or take a night or two
Everybody knows you've been discreet
But there were so many people you just had to meet
Without your clothes
And everybody knows
There's lines about doing cocaine having lots of casual sex and about a plague coming and it came out in the 1980's when AIDS was a new crisis.
The last verse seems very self-referential
And everybody knows that you're in trouble
Everybody knows what you've been through
From the bloody cross on top of Calvary
To the beach of Malibu
Everybody knows it's coming apart
Take one last look at this Sacred Heart
Before it blows
And everybody knows
Every verse concludes with "everybody knows", preceded by a line that rhymes with "knows", and none of them suck. He uses the idea of fucked up things that we all deal with to expand the content of the song so that it winds like streamers around a maypole, expanding out to hierarchy, racism and materialism, but still somehow keeping within a single conceptual place.
With a much more specific meaning is the early Wailers song 400 Years. It's on their first major label record, I think: Catch a Fire. Either that or Burnin', which was the second. It's lyrics are the chanting style, with call and response echoing
400 years (400 years)
400 years (400 years)
And it's the same philosophy
Those early Wailers songs are full of meaning, message, allegory and symbolism.
If you are a big tree, we have a small axe, sharpened to cut you down. Sharpened to cut you down.
There were three big record companies or radio stations or something in Jamaica, refereed to as the "big three". So clever. That's another one with a mini-verse style chorus (number two in the above list).
Often we as songwriters have a melody we'd like to sing and want to find words that fit. Or simply have a chord progression that we want to play, but it feels like it needs some accompaniment. So now we need melody AND words.
I often feel that a great song, stands on it's own with just a single voice. Therefore, starting with a melody and/or words is probably a stronger foundation than starting with a riff.
However, tons of great songs are in fact based partially or wholly on riffs. For example, Money by Pink Floyd. Flashlight by Bernie Worrell and Parliament Funkadelic, I Feel Good by James Brown.
That brings to mind the idea of songs without choruses or without refrains at all.
- Subterranean Homesick Blues by Bob Dylan
- Space Oddity by David Bowie
- check this whole list
I'd be interested to hear your input on other types of refrains and songs that you think of reading this.
Thanks to 
See you around soon. I hope. As James Brown says
Keep on singin' (repeat)