Away goals rule

The Away goals rule is a way of breaking ties in association football when two teams played two legs and once at each team's homeground. The rule says that the team that scored the most "away from home" is awarded the win. This rule is used in the UEFA Champions League, UEFA Europa League, FIFA World Cup qualification, CONCACAF Champions League, MLS Cup playoffs, AFC Champions League, AFC Cup, Copa Libertadores, Copa Sudamericana, CAF Champions League, CAF Confederation Cup, Liga MX playoffs, Football League Cup semifinals and Football League play-offs semifinals.
Example.
A real life example would be in the 2011–12 UEFA Champions League, where Marseille and Inter Milan were playing in the Round of 16. Marseille won the first leg 1–0 at home, and lost the second leg 1–2. Because they were away from home, and they scored one goal (unlike Inter Milan, as they didn't score a goal when they were away from home), they won the match on away goals.