When I was reading an article, I found that it describes the EEG signal as a high-density signal. So what is that mean?
EMG is high temporal resolution and moderate spatial resolution (comparable to high-density EEG)
"High-density EEG" refers to the number of electrodes in the array. Typically, any EEG rig with more than 64 electrodes is considered to be high-density electroencephalography.