Maximum transmission unit is the largest packet size a particular link can carry without a different fragmentation or handling arrangement. Paths can involve links with different limits, so endpoints need a suitable effective packet size. MTU problems can affect some connections or resources while leaving simpler traffic working, but they require careful diagnosis rather than random tuning.
A practical example
A tunnel or another network arrangement can reduce the size available for carried packets. If size discovery or handling fails, certain transfers may stall even though basic connectivity appears normal through the same general internet connection on the viewing device.
A common misunderstanding
Changing MTU blindly can introduce new problems and obscure the cause. Use documented guidance for the actual network arrangement and retain the original setting for a controlled comparison.
Related terms
Stable technical definition. Editorial approach