It is merely "a goal."
There is none, but I understand what you're asking. It's a goal scored in overtime.
It can be called a Golden Goal, depending on the rules. It can also be called the game winner if the rules are to play the whole overtime.
This remains the longest game in NHL history. The winning goal was scored by Modere "Mud" Bruneteau at 116:30 of overtime.
Russ Courtnall scored the series clinching goal at 5:26 of the second overtime
He scored it at 12:20 OT.
According to FIFA rules, a goal scored in extra time is no different than a goal scored in regulation. The word you are probably looking for is "golden goal," in which extra time ends at the scoring of the goal. This is a rule modification that many leagues implement but is not sanctioned by FIFA.
20 minutes, and every subsequent overtime until a goal is scored
Travis Green in double overtime
Brian Skrudland of the Montreal Canadiens scored the quickest overtime goal in the history of the Stanley Cup Finals when he scored on a 2-on-1 breakaway just 9 seconds into overtime in Game 2 of the 1986 series to beat the Calgary Flames 3-2. An NHL record that still stands tall today.
A goal scored in extra time (overtime) is a goal, and counts toward the final score just the same as a goal scored in regular time. Some competitions make use of the "golden goal", a sudden-death scoring method to quickly determine a winner, but this method is not approved by FIFA.