Hazuki Nakamura wrote:

But is that "more fat" the marbling? Or is it all that fat I cut off the
sides?

Marbling is the flecks (not streaks) of fat in beef. You do want to trim the
exterior fat, while leaving a small band around the edge. That renders down
during cooking and gives the steak more flavor. If trimmed down properly, what's
left is eaten with the beef, again for flavor.

There are plenty of You Tube videos on this...