It is Musarrat Nazir's famous Punjabi folk song 'Mera Laung Gawacha' from 1993 film 'Dulari' which is revamped in Rajkummar Rao and Nargis Fakhri film '5 Weddings' and the classic number is reprised mildly with more beats and slightly high energy.
Every one is dancing to this number performed by Saru Maini who marks her singing debut in Bollywood. The song has an elated Nargis who is curious about Indian traditional marriages,while a shy Rao explains her the myth to this tradition. The crowd is dancing with a euphoric vibe that fills everyone with happy faces and even Saru Maini features in this reprised version. Although there is also a Nucleya version of the song full of EDM beats, while this one is a mild reprise. Click here to watch Laung Gawacha song from '5 Weddings'.
Saru Maini who has performed this iconic number is also making an appearance in the film. On working in the film '5 weddings' along with Rajkumar Rao and Nargis Fakhri, she said "I used to sing at my friends sangeet ceremonies. I would change the lyrics and the tunes of Punjabi folk songs and perform on them for which I was really popular. That's exactly what my role turned out to be in 5 weddings. I play a wedding singer in the film and all the songs have been sung by me. One of the promotional songs 'Laung Gawacha' is based on Punjabi folk music and you'll be watching it on TV courtesy T Series."