| otherwise known as Polon, Vertical Bar, Pipe or "That broken line thingy"
It's used extensively in math for all sorts of things, but if you want to learn about that I suggest you google it or something.
I more know it by the name of the pipe character, because that's what it was called on a forum once, and it took me ages to eventually work out what it actually did, in the simplest way I can think of describing it, the command basically takes whatever the output of the first command is and pass it to the next. So in the terminal (Mac as well as Linux) it is used somewhat like this
comand1 | command2
So in a kinda practical example without talking about grep, say command1 checks if a directory exists and outputs either true or false and then command2 takes either true or false and if true it will make a file called something.txt so combining these commands will check if the directory exists and if it does it will create the file. Understanding this character is kinda a requirement for learning your way around the terminal, and as such if you're interested but didn't quite understand feel free to send me a message and I'll message back eventually
#project hail mary
#lana del rey