website: Clarify `locals` vs. `local.thing` distinction

The subtle difference in keywords when creating vs. accessing locals trips
people up, even more than the "variable" vs. "var" distinction. It deserves its
own subheader on the page, plus a nice noisy callout.

website/docs/configuration/locals.html.md

@@ -14,13 +14,15 @@ earlier, see
 [0.11 Configuration Language: Local Values](../configuration-0-11/locals.html).
 
 A local value assigns a name to an [expression](./expressions.html),
-allowing it to be used multiple times within a module without repeating
+so you can use it multiple times within a module without repeating
 it.
 
-Comparing modules to functions in a traditional programming language:
+If you're familiar with traditional programming languages, it can be useful to
-if [input variables](./variables.html) are analogous to function arguments and
+compare Terraform modules to function definitions:
-[outputs values](./outputs.html) are analogous to function return values, then
+
-_local values_ are comparable to a function's local temporary symbols.
+- [Input variables](./variables.html) are like function arguments.
+- [Output values](./outputs.html) are like function return values.
+- Local values are like a function's temporary local variables.
 
 -> **Note:** For brevity, local values are often referred to as just "locals"
 when the meaning is clear from context.
@@ -37,10 +39,9 @@ locals {
 }
 ```
 
-The expressions assigned to local value names can either be simple constants
+The expressions in local values are not limited to literal constants; they can
-like the above, allowing these values to be defined only once but used many
+also reference other values in the module in order to transform or combine them,
-times, or they can be more complex expressions that transform or combine
+including variables, resource attributes, or other local values:
-values from elsewhere in the module:
 
 ```hcl
 locals {
@@ -51,24 +52,32 @@ locals {
 locals {
   # Common tags to be assigned to all resources
   common_tags = {
-    Service = local.service_name #notice it's "local," no "s."
+    Service = local.service_name
     Owner   = local.owner
   }
 }
 ```
 
-As shown above, local values can be referenced from elsewhere in the module
+## Using Local Values
-with an expression like `local.common_tags`, and locals can reference
+
-each other in order to build more complex values from simpler ones.
+Once a local value is declared, you can reference it in
+[expressions](./expressions.html) as `local.<NAME>`.
+
+-> **Note:** Local values are _created_ by a `locals` block (plural), but you
+_reference_ them as attributes on an object named `local` (singular). Make sure
+to leave off the "s" when referencing a local value!
 
 ```
 resource "aws_instance" "example" {
   # ...
 
-  tags = local.common_tags #notice it's "local," no "s."
+  tags = local.common_tags
 }
 ```
 
+A local value can only be accessed in expressions within the module where it
+was declared.
+
 ## When To Use Local Values
 
 Local values can be helpful to avoid repeating the same values or expressions

website/docs/configuration/variables.html.md

@@ -22,6 +22,13 @@ set their values using CLI options and environment variables.
 When you declare them in [child modules](./modules.html),
 the calling module should pass values in the `module` block.
 
+If you're familiar with traditional programming languages, it can be useful to
+compare Terraform modules to function definitions:
+
+- Input variables are like function arguments.
+- [Output values](./outputs.html) are like function return values.
+- [Local values](./locals.html) are like a function's temporary local variables.
+
 Input variable usage is introduced in the Getting Started guide section
 [_Input Variables_](https://learn.hashicorp.com/terraform/getting-started/variables).
 
@@ -100,6 +107,9 @@ Within the module that declared a variable, its value can be accessed from
 within [expressions](./expressions.html) as `var.<NAME>`,
 where `<NAME>` matches the label given in the declaration block:
 
+-> **Note:** Local values are _created_ by a `variable` block, but you
+_reference_ them as attributes on an object named `var`.
+
 ```hcl
 resource "aws_instance" "example" {
   instance_type = "t2.micro"
@@ -107,7 +117,7 @@ resource "aws_instance" "example" {
 }
 ```
 
-The value assigned to a variable can be accessed only from expressions within
+The value assigned to a variable can only be accessed in expressions within
 the module where it was declared.
 
 ## Type Constraints