Pure Data (Pd) is a real-time graphical programming environment used for audio, video, and graphical processing. In this case, it was used to build a synthesizer instrument.

The oscillator indicates the type of waveform that will be used to create the sound. Each wave has different sonic characteristics. Here, we have a sine wave, triangle wave, and saw wave.

A synthesizer is an electronic musical instrument that generates audio signals. These instruments create sounds by generating waveforms through methods like subtractive synthesis, additive synthesis, and frequency modulation synthesis. Synthesizers can be played with keyboards, controlled by sequencers, software, or other instruments, and may be synchronized via MIDI. They've been used in various contexts, from live music performances to sound effects and composition.