A trimmed flight condition is perhaps best thought of as an equilibrium condition. The simplest trim condition is straight-and-level flight, in which the forces (weight, propulsive, aerodynamic) balance and the moments (aerodynamic and propulsive) sum to zero3.

In this particular trim, the accelerations and angular accelerations are all zero. An aircraft could also be trimmed in a steady banked level turn, a climb, a powered descent, though note that (for example) in a steady turn, the forces and moments will not be balanced because a resultant force and a resultant moment are required to provide the necessary centripetal acceleration (rate-of-change of momentum) and the necessary precession of the angular momentum vector (rate-of-change of angular momentum).