In Patchwork, shape refers to a waveform. For example, on the LFO Modulator device, you can select the shape of the oscillation wave pattern that the LFO will output.
Different shapes produce different effects. Another example is on the Drum Sequencer, where you have a shape knob for each sample that you can adjust the waveform for. This makes it possible to do things like cutting off the release of the drum sound for a gated reverb effect.