The term "sigma-delta" refers to a type of analog-to-digital converter (ADC) that uses oversampling and noise shaping to convert analog signals into digital form. This method allows for high-resolution measurements by sampling the input signal at a much higher rate than the Nyquist rate, effectively reducing quantization noise. In a sigma-delta ADC, the input signal is first integrated and then compared to a reference level, producing a bitstream of 1s and 0s. This bitstream is then filtered and decimated to produce a high-quality digital output. Sigma-delta converters are commonly used in applications like audio processing and sensor data acquisition.