An empty net goal, or colloquially an empty netter, occurs in several team sports when a team scores a goal into a net with no goaltender (goalie) present. Also, if a goalie is pulled and the other team scores the goalie is not credited with a goal against them.
Empty net goals usually occur in one of two different occasions in ice hockey:
Empty net goals are charged to the goaltender that was previously in net as empty net goals against (abbreviated as EN, ENG or ENA). Empty net goals do not count against a goaltender's goals against average or their save percentage, but rather are tracked separately. A goaltender can, however, be credited with a loss as the result of an empty net goal (for example, if a team is trailing by one point, pulls its goalie, concedes an empty net goal, but then scores another but does not score a tying goal before time expires; since no goaltender was on the ice for the game winning goal, the loss is pegged to the last goaltender on the ice). In an unusual case, goaltender Adam Wilcox, in his lone NHL appearance to date, did not concede a goal but was credited with the loss because of the aforementioned scenario.
An empty net goal can occur in soccer in a situation where a team is losing by a goal late in a game in which goal difference is not a relevant factor, such as in a knockout cup competition. Often in these situations the goalkeeper of the losing team will go into the attacking area of his team during a set piece, such as a corner kick. In this case it is then possible for the defending team to score into the empty net if they are able to win possession of the ball.
Examples of this include Xabi Alonso scoring for Liverpool against Luton Town in the FA Cup, Ryan McCann scoring for Queen of the South against Dundee in the Scottish Cup,, Son Heung-min scoring for South Korea against Germany at the 2018 FIFA World Cup and Pity Martínez scoring the last goal of his team against Boca Juniors in the second leg of the 2018 Copa Libertadores Finals at the Santiago Bernabéu Stadium 
With rule changes in the 2010s, the goalie can also be pulled in handball. Unlike the soccer and ice hockey examples, this is not only done in desperate situations near the end of a game, as scoring even on a goal with a goalkeeper in it is easier in handball than ice hockey or soccer. A loss of ball possession and the inability to quickly get a goalie back in time almost always results in empty net goal.