Do “chorus” and “refrain” have different connotations?

According to Ken Stephenson in his What to Listen for in Rock: A Stylistic Analysis, a chorus is a complete section of a song that is repeated, where a refrain is a line or two (often at the end of each verse or the beginning of each chorus) that return throughout the song but don't constitute a separate formal division on their own.

Honestly, I thought that chorus was more about songs and refrain for poems and similar things.

But, as the OALD states, they're synonyms and they both mean "the part of a song or a poem that is repeated after each verse".

My experience as a musician of many years, and after attending a number of songwriter camps (which generally recognize current or contemporary usage of terms) taught by professional songwriters is this: A chorus is understood by most to be as identified in answers and comments above, i.e, a repeating and complete section of a song sung by more than one singer, which typically drives the song's theme and/or is a summation of the song's ideas or point. In industry parlance, it's the "hook". A refrain, however, has a bit more malleable definition. While it can be more or less synonymous with a chorus, it generally means one or two repeating "tag lines" after or between verses, or before a chorus. Some songs have no chorus, and thus the tag lines become the repeating theme or hook. A more modern usage describes a repeating refrain happening just before each chorus as a "pre-chorus", although technically this may be an inaccurate usage of either term.