Jitter

The time or phase difference between the data signal and the ideal clock. 

See NIST SP 800-82 Rev. 2 for more information. 
 
As it relates to queuing, the difference in latency of packets. 

See NIST SP 800-127 for more information. 
 
Non-uniform delays that can cause packets to arrive and be processed out of sequence.

See NIST SP 800-58 for more information.