Fulcrum is a noun that refers to something that plays a central or essential role in an activity, event or situation. 

The Latin word fulcire (full CHEER ay) means ‘to prop up’ or ‘support up.’ When our word of the day first joined the English language in the late 17th century, fulcrum was used to refer to a lever used to support something. This meaning still exists, but today the word is more likely to be used in reference to a role or event that supports something, for example:

The quarterback is generally the fulcrum of any football team. Without his support, the rest of the team has no chance of winning.