Definition
A loading state in which the aircraft's weight is distributed unevenly between the left and right sides of the longitudinal axis, causing one wing to carry more weight than the other. This produces a rolling tendency that the pilot must counter with aileron input, increasing drag and reducing performance.
Plain English
The airplane is heavier on one side than the other, so it wants to roll toward the heavy side and the pilot has to hold the controls against it.
Context Anchor
Seen in weight-and-balance discussions, especially when loading passengers, baggage, or fuel unevenly between the left and right sides of the aircraft.
Derivation
Lateral' comes from the Latin 'latus' meaning 'side.' A lateral imbalance is therefore a side-to-side imbalance, as opposed to longitudinal (nose-to-tail) imbalance.
Why Pilots Care
Requires constant aileron input or trim correction, increases pilot workload, and can mask other control or loading problems.
Analogy
Like carrying a heavy suitcase on one side of your body and having to lean the opposite way to stay upright.
Intuition Check
Do not read “laterally unbalanced” as simply “too heavy.” It specifically means unbalanced from left to right, not front to back and not necessarily over the maximum allowed weight.
Example Sentence 1
Burning fuel from only one wing tank can create a laterally unbalanced condition, so pilots alternate tanks to keep the load even.
Example Sentence 2
After adding ballast to the right wing, the laterally unbalanced condition was corrected and wings-level flight was maintained without trim.