CloudFormation supports these parameter types:
Basic Types:

• String: Text values
• Number: Numeric values
• CommaDelimitedList: List of values separated by commas
  AWS-Specific Types:
• AWS::EC2::KeyPair::KeyName: EC2 Key Pair names
• AWS::EC2::SecurityGroup::Id: Security Group IDs
• AWS::EC2::Subnet::Id: Subnet IDs
• AWS::EC2::VPC::Id: VPC IDs
• AWS::Route53::HostedZone::Id: Route 53 Hosted Zone IDs
  Lists:
• List<Number>: List of numbers
• List<AWS::EC2::Subnet::Id>: List of subnet IDs
  Example:

Parameters:
  Environment:
    Type: String
    AllowedValues: [dev, staging, production]
    Default: dev
  SubnetIds:
    Type: List<AWS::EC2::Subnet::Id>
    Description: Subnets for load balancer
  InstanceCount:
    Type: Number
    MinValue: 1
    MaxValue: 10
    Default: 2