Are "div > p" & "div p" same?

Hey, I've an obvious question.

For code like:

<div>
     <p>We want to format this text :)</p>
</div>

Some people use selector like:

div > p {
     something
}

And others:

div p {
     something
}

What's the difference in this case? In my opinion - none?

And by the way, isn't the descendant item always a child?! What's the difference between the two? I'm reading w3.org but can't get it :)

Thank you!