What is IP Packet Delay Variation (IPDV), also called "jitter"?

IPDV measures the variation in delay of uni-directional, consecutive packets (packet 1 and 2, 2 and 3 etc.) which flow between between two hosts over an IP path. Low IPDV is especially important for applications requiring timely delivery of packets, e.g. multimedia applications, VoIP, video etc. The maximum delay variation is useful for determining the optimal buffer sizes for such applications.

See URL for more information:
http://www.ietf.org/internet-drafts/draft-ietf-ippm-ipdv-10.txt