Understanding contents and workwise of a Terraform plan If you export a Terraform plan, it is a binary file.

Now, calls to a cloud management interface are HTTP calls following corresponding REST APIs. 

Does this mean this internal Terraform format somehow encodes these calls through some enumerations? 

Like, given in the plan it would be, "B#3$1$2" which then translate "call the API function we have given number 3 passing values 1 and 2 as arguments"? 

How does it work?
Terraform use protobuf to store the plans according to its code


  // writeTfplan serializes the given plan into the protobuf-based format used
  // for the "tfplan" portion of a plan file.


You can find here the code generating the plan file.

So in brief that's a binary file with a serialized version of what to do in a portable format (protocol buffers) for which you find more information here