Dadra is either of two separate but originally linked concepts in Hindustani classical music.
This is a Hindustani classical tala (rhythmic cycle), consisting of six beats in two equal divisions of three. The most commonly accepted theka or basic pattern for this tala is dha dhi na, dha tu na. There is a higher emphasis laid on the first swar in comparison the following two, that is, dha - higher emphasis following dhi na and again a higher emphasis on dha following tu na.
In this context dadra is a light classical vocal form in Hindustani classical music, mostly performed in Agra and in Bundelkhand region. It was originally accompanied by dadra tala (from where the term for the genre was borrowed), but later dadra compositions are often found in other light talas (such as keherwa).
The peculiarity of Dadra genre is that the Sthayi is in Braj Bhasha while the Antara is sometimes in Urdu. It is one of the illustrations of how cultures have amalgamated and coexisted in Indian classical music .
There have been some Bollywood songs as well based on the same for instance Madan Mohan (music director) composition -Lag Jaa Gale, a song from the movie Woh Kaun Thi. Then there is also a famous dadra sung by Mallika-e-Ghazal Begum Akhtar Hamari Atariya Pe Aao.