Direct address refers to communicating a message directly to an individual or group by using their name or a pronoun like "you". Nouns used for direct address, called nouns of direct address, are always grammatically separate from the rest of the sentence, functioning like interjections. Nouns of direct address are set off from the rest of the sentence with commas, regardless of their position, to avoid ambiguity. The pronoun "you" also has vocative qualities when used for direct address.

4. In English grammar and rhetoric, direct address
is a construction in which a speaker or writer
communicates a message directly to another
individual or group of individuals.
The person(s) being addressed may be identified
by name, nickname, the pronoun you, or an
expression that's either friendly or unfriendly.
Conventionally, the name of the person (or
group) being addressed is set off by a comma or
a pair of commas.

5.  It is always a proper noun. It does not have any grammatical relationship to
any part of the sentence. It is set off by commas.
 Nouns can serve as nouns of direct address, which means that the noun is
used to refer to someone directly.
 Nouns of direct address are always separated from the rest of the sentence
with a comma. It does not matter where they are in the sentence.
Example:
1) What do you think of this, Georgia?
2) William and Mary, will you make sure you clean up your rooms?
3) I don't know, Grandma, whether I want chicken or fish for dinner.
4) I am sure you didn't mean to break the lamp, Kevin.

6. DIRECT ADDRESS - vocative form
In grammar, the vocative case (abbreviated voc) is
a grammatical case which is used for a noun that identifies a
person (animal, object, etc.) being addressed, or occasionally
for the determiners of that noun.
A vocative expression is an expression of direct address
by which the identity of the party spoken to is set forth
expressly within a sentence. For example, in the sentence "I
don't know, John," John is a vocative expression that
indicates the party being addressed, as opposed to the
sentence "I don't know John" in which "John" is the direct
object of the verb "know".

7.  Nouns of direct address are the nouns used to indicate that a
speaker is directly addressing a person or group. Nouns of direct
address are grammatically separate from the rest of the sentence,
functioning like interjections since they aren’t involved with the
action of the sentence. Nouns of direct address are also known as
vocative case nouns.
 Nouns of direct address don’t need to name people. They can also
name places, things or idea.
 Example:
What Are Nouns of Direct Address?
Rubber duckie,
you’re the one.
You make bath
time lots of
fun.
Oh Christmas
Tree, Oh
Christmas tree,
how lovely are
thy branches.

8. It is important to set these nouns apart from the rest of the sentence with
comma.
Let’s eat Grandpa!
Let’s eat, Grandpa!
As you can see, these two sentences have very different meaning.
Placing of commas:
Mom, this turkey is so amazing! (If it comes before the sentence, put a
comma after it)
This turkey is so amazing, Mom! (If it comes after the sentence, put a
comma before it)
This turkey, Mom, is so amazing! (If it comes in the middle of the
sentence, put a comma around it)

9. Direct Address and the Pronoun 'You'
"It is clear that a term of address is always closely linked
with the pronoun 'you,' which in itself
has vocative qualities.
One could say, in fact, that whenever pronominal 'you' is
used in direct address, vocative 'you' is implicitly
present. The two kinds of 'you' are inextricably bound
together, though in an utterance like 'You! What do you
think you're doing!' the first 'you' is clearly vocative, where
the others are pronominal.