What does epoch mean in EEG?
EEG epoching is a procedure in which specific time-windows are extracted from the continuous EEG signal. These time windows are called “epochs”, and usually are time-locked with respect an event e.g. a visual stimulus. 

If your EEG data are in a matrix [channel x time] where time is the complete continuous EEG signal, after the epoching procedure you should have a matrix [channel x time x epochs] where time is the time length of each epoch, and epochs is the number of segments you extracted from continuous EEG signal. 

Finally, if you want to extract epochs from your signal, you should know what are the segments of interest to be analyzed, for instance, a specific stimulus.