Merge pull request #31508 from wzyboy/docs/unknwon-value

docs: fix typo regarding unknown values

website/docs/language/expressions/references.mdx

@@ -326,12 +326,10 @@ values are decided dynamically by the remote system. For example, if a
 particular remote object type is assigned a generated unique id on creation,
 Terraform cannot predict the value of this id until the object has been created.
 
-To allow expressions to still be evaluated during the plan phase, Terraform
-uses special "unknown value" placeholders for these results. In most cases you
-don't need to do anything special to deal with these, since the Terraform
-language automatically handles unknown values during expressions, so that
-for example adding a known value to an unknown value automatically produces
-an unknown value as the result.
+Terraform uses special unknown value placeholders for information that it
+cannot predict during the plan phase. The Terraform language automatically
+handles unknown values in expressions. For example, adding a known value to an
+unknown value automatically produces an unknown value as a result.
 
 However, there are some situations where unknown values _do_ have a significant
 effect:
@@ -357,4 +355,4 @@ effect:
   types where possible, but incorrect use of such values may not be detected
   until the apply phase, causing the apply to fail.
 
-Unknown values appear in the `terraform plan` output as `(not yet known)`.
+Unknown values appear in the `terraform plan` output as `(known after apply)`.