A credential that identifies an AWS account or user to AWS (such as the AWS secret access key).

Amazon Simple Storage Service (Amazon S3), Amazon EMR: The unique identifier for an object in a bucket. Every object in a bucket has exactly one key. Because a bucket and key together uniquely identify each object, you can think of Amazon S3 as a basic data map between the bucket + key, and the object itself. You can uniquely address every object in Amazon S3 through the combination of the web service endpoint, bucket name, and key, as in this example: http://doc.s3.amazonaws.com/2006-03-01/AmazonS3.wsdl, where doc is the name of the bucket, and 2006-03-01/AmazonS3.wsdl is the key.

AWS Import/Export: The name of an object in Amazon S3. It's a sequence of Unicode characters whose UTF-8 encoding can't exceed 1024 bytes. If a key (for example, logPrefix + import-log-JOBID) is longer than 1024 bytes, AWS Elastic Beanstalk returns an InvalidManifestField error.

IAM: In a policy, a specific characteristic that's the basis for restricting access (such as the current time or the IP address of the requester).

Tagging resources: A general tag label that acts like a category for more specific tag values. For example, you might have EC2 instance with the tag key of Owner and the tag value of Jan. You can tag an AWS resource with up to 10 key–value pairs. Not all AWS resources can be tagged.

AWS Glossary