It's about signals (streams of data) and what happens to them when they pass through systems (things that transform signals).

This might be more helpful, though.

A list of signals and systems that act upon them

  1. A picture and a photoshop filter.
  2. Music from an electric guitar and the wah pedal that bends the sound on the way to your amp.
  3. The bumps on the road your bike runs over and the dampening effects of the shock absorbers, tires, seats, and tubes that keep your bottom from being rattled sore.
  4. The flame of an erratically sputtering camping stove passing through the thick metal of your dutch oven so that your potatoes experience a slow, steady warmth.
  5. The retinal image you have of an initially dark classroom when someone suddenly flicks the lights on, and the actions taken by your eyes and brain so that you can see again in the blinding, blinding photon flood.
  6. A hungry frog watching for the fast black dot of a fly against the slow, waving background of leaves in the wind.
  7. This is somewhat sketchier: lots of student feedback on the recent occurrences in a course, and the winnowing and distillation process the professor needs to do with this input so they can make long-term corrections to address it.
  8. A piano with broken keys, so that it only plays some of the notes you press down.