Line Dancing is a particular group of dance that includes any choreographed dance where people dance in a line, or in a row. Conga counts as a line dance, but so does country western dances, polka, swing, and even the more traditional, formal versions of the waltz!
This type of dance became popular in the 90s, especially in the United States, due to the popular hit “Don’t Tell My Heart” by Billy Ray Cyrus; but nowadays it is has faded out and it is not popular anymore.
If you want to practice line dancing, there are some dance schools that offer lessons in polka and country western dance: check Google to see if there is any nearby you as they are rather rare. If you want to enjoy dancing in public, country clubs or western-style Texan pubs will every once in a while hold dances where you can put your skills to test!