What singer and/or group defined 1970s music?

None because it was a transiton period with a few different competing styles that where popular.. For instance Disco and Metal and Pop music all had large numbers of followers..

You could give an example of one artist for each type..

Pop: Elton John or ABBA or Queen
Metal: ACDC or Pink Floyd or Aerosmith
Disco: Bee Gees or The Jacksons

I have to include the Electric Light Orchestra as they where may favorite artists in the early 70's they had their own unique style Orchestral rock..

Some good ones already mentioned.
Fleetwood Mac; The Eagles etc.

Maybe I'd add Pink Floyd; Steely Dan; Queen; Jethro Tull; Blondie; Yes;.... probably others

Eagles

Depends on what kind of music one liked. Lots of people name rock groups, but there were all kinds of popular music during that time.

One genre that was pretty specific to the 70s was disco.

All depends on your taste in music, I guess. I mostly think of JUDAS PRIEST, KROKUS, etc.

I would have to say the BeeGees and ABBA

I was really into jazz/rock fusion at that period.

Fleetwood Mac

Which genre?

One of the many Bands 1964-1970 Hermans Hermits

[media=https://youtu.be/F0RrC_n-OTc]

Led Zeppelin's arena cock rock, Pink Floyd, Queen, Eagles, Genesis, Rush, Jethro Tull, Fleetwood Mac, Deep Purple, Black Sabbath, so many of them 😍

Late 1970, I think ABBA.

David Bowie

Neil Young.

Fleetwood Mac

Fleetwood Mac - TUSK

[media=https://youtu.be/NKCucBUWx5o]

Carole King

Theres wayyyy too many

Elton John, Linda Ronstadt

Fleetwood Mac - the Chain

[media=https://youtu.be/kBYHwH1Vb-c]

Plant and led zep

U3

ABBA, Boston, ELO, Aerosmith, Black Sabbath, Starlight Vocal Band, Carpenters, KISS, David Bowie, Buggles, Runaways, Blondie, and so many others.