Pattern degradation was a process during the transport process by which an object or a living organism lost its alignment in a matter stream and, as such, correct arrangement of the object or living organism became impossible during pattern reintegration.
During a refit of the USS Enterprise in the 2270s, Commander Sonak and a female officer died when their patterns degraded during transport. (Star Trek: The Motion Picture)
In 2294, the USS Jenolan crash-landed on a previously undiscovered Dyson sphere. The only survivors were Captain Montgomery Scott and Ensign Matt Franklin. With dwindling supplies, Scott developed an idea to place the two of them in transporter suspension until they could be rescued. They remained within the transporter buffer for the next 75 years until they were discovered by the USS Enterprise-D. Scott was successfully rematerialized but Franklin's pattern had degraded by 53%, effectively killing him. (TNG: "Relics")