What does Type: AWS::EC2::Subnet mean?

Type:AWS::EC2::Subnet does not understand the meaning of :.

For example, Key:name indicates that the key value is name.

However, Type:AWS::EC2::Subnet has two :s, and I looked for a different meaning than above, but I couldn't find a clear answer.

It's just a guess, but I thought it was expressing nesting.
(Type is RouteTable for EC2 in AWS)

However, I thought that the nesting of YAML is different because it is expressed as follows.

AvailabilityZone: !Select 
- 0 - !GetAZs 
Ref: 'AWS:: Region'

I would appreciate it if you could point out whether or not you think wrong.
Thank you for your cooperation.