The Key-Pairs are password-protected login credentials for the Virtual Machines that are used to prove our identity while connecting the Amazon EC2 instances. The Key-Pairs are made up of a Private Key and a Public Key which lets us connect to the instances.

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"Parameters" : {

    "KeyName": {

      "Description" : "Name of an existing EC2 key pair for SSH access to the EC2 instance.",

      "Type": "AWS::EC2::KeyPair::KeyName"

    },

https://docs.aws.amazon.com/servicecatalog/latest/adminguide/getstarted-keypair.html