In digital signal processing, downsampling takes high-resolution data recorded at a high sampling rate and compresses the data into a smaller bandwidth and sample rate. The original signal is passed through a low-pass filter, reducing the frequencies above and below a certain threshold and keeping only every few samples, creating an approximation of the signal at the lower frequency.
This is a companion discussion topic for the original entry at https://www.edgeimpulse.com/blog/introducing-downsampling-for-time-series-data