Confluence'' is the word used to denote the place where two or more water bodies meet, may be it that a tributary meets the main river or two rivers meet to form a new river, or three or four rivers meet at a point.
While in Hindi it is denoted by 'Prayag'. Sanskrit word being, 'Sangam'.
"Panch Prayag" is the famous five confluences of rivers in Himalayas.
Here is a map showing, the position of the five confluences holy to Hindus.
1] Vishnuprayag : Confluence of Dhauli Ganga and Alaknanda.
2] Nandaprayag : Confluence of Nandakani and Alaknanda.
3] Karnaprayag : Confluence of Pindar and Alaknanda.
4] Rudraprayag : Confluence of Mandakani and Alaknanda.
5] Devprayag : Confluence of Bhagirati and Alaknanda.