Jitter are timing differences. A digital transport reads the data on a CD. The data has a sequence. To encode the sequence, timing data is embedded along with the music signal data on a CD. The "recovered clock" read from the CD by the transport is then conveyed to a clock in the digital converter to convert the digital signal into analog electrical info a preamp can use. Like all things audio, the initial reading, the conveyance and the conversion are imprecise. The more imprecise the match up between the music data and its intended timing sequence, the more jitter. The more jitter the edgier the music sounds.
