What is the meaning of "Current player sessions" in the metrics?

I thought “Current player sessions” means how many players are in the game but it isn’t matched.
What does it mean exactly?

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Its the number of actual player sessions active.

Player sessions with either ACTIVE status (player is connected to an active game session) or RESERVED status (player has been given a slot in a game session but hasn’t yet connected). This metric can be used with automatic scaling.

See Monitor GameLift with Amazon CloudWatch - Amazon GameLift