Translation:We saw lots of colorful fish in the Red Sea.
The literal meaning of ים סוף is "Sea of Reed", (or more naturally "the Sea of Reeds/the Reed Sea". This is the sea that Moses and the Israelites split. I've heard that in Greek as well as in English, there is only one letter of difference between red and reed, so it was easy to conflate the reed sea and the Red Sea (the sea stretching down from Eilat), so for a long time both the sea the Israelites crossed and the well-identified Red Sea were given the same name and thought to be the same thing. So even in Hebrew now הים האדום can be referred to as ים סוף. But no one is actually sure if this is the sea that the Israelites crossed and it probably isn't.
If I recall correctly, the best estimate based on the information given in the תנ"ך and especially what's in the תורה is that ים סוף is/was a large lake somewhere north of the Gulf of Suez, possibly one that has since dried up. I don't have a strong enough grasp of the geography to know more than that, though I have a strong enough grasp of the story to know that the body of water had to be large enough that the people couldn't just go around it.
There's an excellent essay on this topic by Nahum Sarna in both his book, https://www.amazon.com/Exploring-Exodus-Origins-Biblical-Israel/dp/0805210636, and in the JPS Torah Commentary.