Kelp vs Seaweed What’s The Difference

https://www.growertoday.com/kelp-vs-seaweed/ What is the difference between kelp vs seaweed? And why are they used as fertilizer? Isn’t kelp a seaweed? What form should I pick (seaweed powder or liquid extract)? I ask myself all those questions when I look at the different organic and/or natural fertilizers available in the gardening market. #seaweed #kelpseaweed #kelpvsseaweed