Botellón is a custom that takes place in Europe (mainly spain) which involves the gathering of a large number of young people mostly between the ages of 16 and 24. They gather outdoors to drink beverages previously acquired in shops (usually supermarkets), to listen to music and talk. This is often done because of the high prices in bars and being underage for bars and clubs.
'Hey Man, you coming out later for our el botellon'
'Were all meeting in a bit for a el botellon'