Learn Hardcore Korean: geu bubuneun jumalmada gongwoneseo sanchaekhaeyo. - That couple takes a walk in the park every weekend.

Breakdown of geu bubuneun jumalmada gongwoneseo sanchaekhaeyo.

What does 그 mean in 그 부부는? Is it that or the?

In this sentence, 그 literally means that, but in natural English it can often feel like the depending on context.

그 부부 = that couple
In context, it may also be understood as the couple if both speakers already know which couple they mean.

Korean often uses 그 to point to something already mentioned or already known in the conversation.

What exactly does 부부 mean?

부부 means a married couple or husband and wife as a pair.

A few useful notes:

부부 refers to the two people together as one unit.
It does not mean just any couple dating each other.
You do not need a separate plural marker here. Korean often leaves plurality unmarked when it is already clear.

So 그 부부는 means as for that married couple...

Why is the particle 는 used after 부부?