What does the term "class act" mean? For example, The club is lucky to have such a class act and he is lucky to have the club. What does "class" and "act" mean respectively in this set phrase or word combination of "class act"? Does "class" here as the adjective modify the noun "act"?
The phrase itself is highly contextual. Sometimes it's used as a high compliment for someone who is respectable and gracious:
Coach Eaves was a class act. I really admire coaches who do it right, don't go crazy on the sidelines, and set a good example for others.
(Rick Wood, 40 Seasons: The Life of a High School Basketball Coach, 2011)
Most guys would have forgotten all about a minor moment like that, but not Jimmy Stewart. He was a class act all the way.
(Tony Curtis, American Prince: A Memoir, 2008)
Sometimes it's used to describe someone's stylistic appearance, or someone who has both intelligence and charm:
She was a very serious student, both intelligent and beautiful. As they say, she was a class act. To get her attention or a smile from her was extremely hard. She had utter self-confidence, great poise, and an elegant walk.
(Vartan Gregorian, The Road to Home: My Life and Times, 2008)
Sometimes it's used to describe someone's overall classiness, in a way that sets them apart from their peers:
She was a class act. He was used to hanging around with floozies, but his taste was changing. He liked the air of eloquence that rested on her.
(Inez Brinkley, Embracing the Light, 2006)
Janelle had street sex appeal, the stark sexuality of a cocktail waitress exposing some tits and ass as she bends over to serve your drink. But this dame was a class act, a woman wrapped in pearls and sable getting out of a Rolls Royce. My first impression of her was of a cheetah with a diamond choker...
(Harold Robbins, Sin City, 2003)
In the context you mention:
The club is lucky to have such a class act...
I'd intepret that to mean that whatever act is performing wouldn't necessarily be expected to be seen in such a venue. Perhaps it's a folk singer with the voice of an angel playing in a dingy nightclub, but the expression could be used to describe a variety of circumstances.
In the setting of a club, I'd interpret a class act to be something that is more refined than raw, more sophisticated than cheesy. I would expect the performance to have broad appeal to a wide audience, as opposed to a niche act. I would expect the class act to be more stylishly dressed than other performers at the club.
I believe that the term comes from vaudeville. It was used to describe an act that was related to or would appeal to the upper classes, such as opera, classical singing or other refined entertainment. A manager might say, "That routine is a class act" as opposed to quirky odd or low brow stuff. So it then came to be used to describe someone acting in a gracious way, as would be attributed to an upper class person, kind of like saying someone is a "real gentleman" Literally meaning they are notacting like a low class guy but an upper class person. Insulting to working clas people but there you go. OF course, it is funny when someone uses it sarcastically. "Yeah, a real class act, ya jerk"
It means that the artist's performance was of high quality.
The phrase a class act, in a strict sense indeed means that the performer/artist put on an exceptionally good show. Oh, and yes, class is an adjective here.
However, nowadays I'd say its used whenever somebody does something memorable. Regardless of it being particularly good. If Keith Moon were still alive today, and he'd drive 3 rolls royce's into a public swimming pool dressed as a Japanese schoolgirl, that's exceptionally mad, even for him. So it'd be another Keith-Moon style class act.
A class act can also be used to indicate irony or sarcasm. Sort of like saying:
Your drunken singing in the underground was a real class act
So, in response to J.R. on the sex pistols, I wouldn't find it strange if a review stated that: "Their show was a real class act, eventually Johnny Rotten himself had to tell Sid to cool it".
Obviously, from a musicians stand-point punk is no class act. Exciting? possibly, but certainly not great challenge. Fighting on stage, or being to stoned to stay upright is no class act either. What this fictional review is saying is that their performance, even by their own standards, was one of their most extreme, over the top, violent shows ever. A real class act.