Collection Types
A collection type allows multiple values of one other type to be grouped together as a single value. The type of value within a collection is called its element type. All collection types must have an element type, which is provided as the argument to their constructor.
For example, the type list(string) means "list of strings", which is a different type than list(number), a list of numbers. All elements of a collection must always be of the same type.
The three kinds of collection type in the Terraform language are:
* list(...): a sequence of values identified by consecutive whole numbers starting with zero.
The keyword list is a shorthand for list(any), which accepts any element type as long as every element is the same type. This is for compatibility with older configurations; for new code, we recommend using the full form.
* map(...): a collection of values where each is identified by a string label.
The keyword map is a shorthand for map(any), which accepts any element type as long as every element is the same type. This is for compatibility with older configurations; for new code, we recommend using the full form.
* set(...): a collection of unique values that do not have any secondary identifiers or ordering.
https://www.terraform.io/docs/configuration/types.html
Structural Types
A structural type allows multiple values of several distinct types to be grouped together as a single value. Structural types require a schema as an argument, to specify which types are allowed for which elements.
The two kinds of structural type in the Terraform language are:
* object(...): a collection of named attributes that each have their own type.
The schema for object types is { <KEY> = <TYPE>, <KEY> = <TYPE>, ... } - a pair of curly braces containing a comma-separated series of <KEY> = <TYPE> pairs. Values that match the object type must contain all of the specified keys, and the value for each key must match its specified type. (Values with additional keys can still match an object type, but the extra attributes are discarded during type conversion.)
* tuple(...): a sequence of elements identified by consecutive whole numbers starting with zero, where each element has its own type.
The schema for tuple types is [<TYPE>, <TYPE>, ...] - a pair of square brackets containing a comma-separated series of types. Values that match the tuple type must have exactly the same number of elements (no more and no fewer), and the value in each position must match the specified type for that position.
For example: an object type of object({ name=string, age=number }) would match a value like the following:
{
name = "John"
age = 52
}
Also, an object type of object({ id=string, cidr_block=string }) would match the object produced by a reference to an aws_vpc resource, like aws_vpc.example_vpc; although the resource has additional attributes, they would be discarded during type conversion.
Finally, a tuple type of tuple([string, number, bool]) would match a value like the following:
["a", 15, true]
https://www.terraform.io/docs/configuration/types.html

terraform init command is used to initialize a working directory containing Terraform configuration files. Reference: https://www.terraform.io/docs/cli/commands/init.html

Explanation
The terraform taint command manually marks a Terraform-managed resource as tainted, forcing it to be
destroyed and recreated on the next apply.
This command will not modify infrastructure, but does modify the state file in order to mark a resource as
tainted. Once a resource is marked as tainted, the next plan will show that the resource will be destroyed and
recreated and the next apply will implement this change.
Forcing the recreation of a resource is useful when you want a certain side effect of recreation that is not
visible in the attributes of a resource. For example: re-running provisioners will cause the node to be different
or rebooting the machine from a base image will cause new startup scripts to run.
Note that tainting a resource for recreation may affect resources that depend on the newly tainted resource. For
example, a DNS resource that uses the IP address of a server may need to be modified to reflect the potentially
new IP address of a tainted server. The plan command will show this if this is the case.
This example will taint a single resource:
$ terraform taint aws_security_group.allow_all
The resource aws_security_group.allow_all in the module root has been marked as tainted.
https://www.terraform.io/docs/commands/taint.html

Explanation
Terraform is built on a plugin-based architecture. All providers and provisioners that are used in Terraform configurations are plugins, even the core types such as AWS and Heroku. Users of Terraform are able to write new plugins in order to support new functionality in Terraform.
https://www.terraform.io/docs/plugins/basics.html

Every provider has its own required and allowed declarations none of which match between cloud providers.