Why Decimation lowers the effective sample rate of a digital data stream by keeping only every Nth sample and discarding the rest. A decimation factor of 10, for example, turns a 100 kHz sample stream into a 10 kHz stream, which cuts the processing load and data storage needed downstream. It is normally preceded by a low-pass (anti-alias) filter, because after decimation the new Nyquist limit is half the reduced sample rate, and anything above it would fold back as an alias.
Watch out The choice about removing significant digits describes reducing bit depth or word length, which changes amplitude resolution, not sample rate; decimation throws away samples in time, not bits of precision.
Decimate = drop samples, not bits. Roman decimation killed every tenth man; DSP decimation keeps every tenth sample.