This picture above is a giant.
What exactly is the difference between a "giant" and the Hebrew "nephilim"?
Well, for one the English term "giant" is vague and generic: it merely means taller than average which is why a pro basketball player can be called giant (and none of them even make it to 8 ft.) and folkloric tales of people many entire body lengths taller than average are also called giants. The answer is that Genesis 6 is the only reliable reference to Nephilim and it provides us no physical description of them at all. Also, the image you have is of Goliath but he was either just shy of 7 ft. or just shy of 10 ft. (depending of Greek or Hebrew manuscripts) but since the average Hebrew male of biblical days was 5.5 ft. (so women averaged even less) then even a 6.5 ft. warrior was a "giant." Lastly, Goliath was a Philistine and they were considered Anakim and there is no relation between them and Nephilim. Plus the problem is that some use the English word "giant" to pseudo-translate both the strictly pre-flood "Nephilim" and the post-flood "Rephaim" and there is no relation between these either.
Merriam-Webster provides the following definition:
a biblical race of giants or demigods
1 : a legendary humanlike being of great stature and strength
2a : a living being of great size
b : a person of extraordinary powers
3 : something unusually large or powerful
This would imply that a Nephilim would be a type of giant.
Should you want more information, please make your question more specific.