For example C172R specifications: Cruise speed:122 knots What does this mean? Maximum achievable Indicated airspeed At specific conditions? Another example - rate of climb: 721 ft/min For what conditions? So much factors can affect this..
Read the POH - it will show the conditions the speed was measured under.
Cruise, 75% Power at 8500 Feet. . . . . . . . . . . . . . . . . . 122 KNOTS
*Speed performance is shown for an airplane equipped with speed fairings which increase the speeds by approximately 2 knots. There is a corresponding difference in range, while all other performance figures are unchanged when speed fairings are installed.
The above performance figures are based on airplane weights at 2450 pounds, standard atmospheric conditions, level, hard-surfaced dry runways and no wind. They are calculated values derived from flight tests conducted by Cessna Aircraft Company under carefully documented conditions and will vary with individual airplanes and numerous factors affecting flight performance.