嵌入式结构还是嵌套结构？

Is the following code is an example of Embedded Struct or Nested Struct or something else? And Are we using one struct type (person) in another type struct (secretAgent) ?

package main

import "fmt"

type person struct {
    first string
    last  string
    age   int
}

type secretAgent struct {
    person
    ltk bool
}

func main() {

    sa1 := secretAgent{
        person: person{
            first: "James",
            last:  "Bond",
            age:   32,
        },
        ltk: true,
    }

    fmt.Println(sa1.first, sa1.last, sa1.age, sa1.ltk)
}

The spec refers to that as an embedded field:

A field declared with a type but no explicit field name is called an embedded field. [...]

struct {
    T1        // field name is T1
    ...
}

I'm not sure what you mean by "using one struct type in another struct type" but you are using person inside secretAgent by embedding one struct type inside another. The person fields are also promoted to behave like members of secretAgent in most cases:

Promoted fields act like ordinary fields of a struct except that they cannot be used as field names in composite literals of the struct.

So you can say:

sa1 := secretAgent{
    person: person{
        first: "James",
        last:  "Bond",
        age:   32,
    },
    ltk: true,
}

and

sa1.first

but not:

sa1 := secretAgent{
    first: "James",
    last:  "Bond",
    age:   32,
    ltk: true,
}

You can also explicitly refer to the embedded person fields through the person:

// As a promoted field...
sa1.first
// More explicitly...
sa1.person.first

It is both embedded and nested struct. And you can the naming convention should follow the first word should be upper case.

package main

import "fmt"

type Name struct{
    first string
    last  string
}

type Person struct {
    name  Name  
    age   int
}

type SecretAgent struct {
    person Person
    ltk bool
}

func main() {

    sa1 := secretAgent{
        person: Person{
            name: Name {
               first: "James",
               last:  "Bond"
            },
            age:   32,
        },
        ltk: true,
    }

    fmt.Println(sa1.person.first, sa1.person.last, sa1.person.age, sa1.ltk)
}