"streaming" is transmitting a live video broadcast online.

A "broadcast" is transmitted by radio or television, over the airwaves. TV and radio waves spread out everywhere in all directions. The word goes back to the 1920s. Before about 1996 or so, you could only send files over the Internet. You could send a sound file or a video file and play them. You had to wait until you'd received the whole file before you could start playing it. In the late 1990s, they developed the technology to send a continuous "stream" of audio and video, that flows from the source to viewers. You can play an hour-long YouTube video and it starts immediately. The next few seconds are transmitted while you are watching the first few seconds. That's "streaming." "Live streaming" means you are watching the audio and video as they are happening, just like a live broadcast. The actual origin of the word "broadcast" is interesting. It means to plant crops by scattering seeds everywhere, as opposed to burying each seed individually.