The pattern buffer is the part of a transporter system that briefly holds a matter stream during beaming, preventing it from degrading before it reaches its destination.
During transport, a subject's pattern passes through the buffer, where it can be held for a short time if a problem arises. Patterns normally degrade quickly, so long-term storage is considered impossible under ordinary conditions.
Montgomery Scott defied that limit after the USS Jenolan crashed on a Dyson sphere. He rigged the transporter to keep himself and a crewmate cycling through the buffer, and he emerged 75 years later aboard the Enterprise-D. His companion's pattern did not survive.