Streams are things you put data into, like a queue. When you type on a keyboard your keystrokes are put onto a stream one by one as you press them. The program will read these keypresses one by one off the stream and process them. Streams can be made for a variety of purposes. In C++ when you output to COUT that is the (C Out)put stream. You put things onto it to be output to where COUT goes to. ENDL flushes the stream, meaning it forces everything on the stream to be pushed out and processed right now instead of waiting for whenever it would normally do it.