The slew of a spacecraft is its orientation in reference to a plane or fixed position such as Earth, the Sun, another celestial body or other point in space.
Keeping a spacecraft slewed properly is vital for ensuring that its antenna remains oriented toward Earth for sending and receiving data and commands.
[4] For spin-stabilized spacecraft, slewing is accomplished by applying a (significant) torque to the spacecraft, in general by operating a thruster in synchronous or asynchronous direction to its spin to adjust its spin rate.
The slew of 3-axis stabilized spacecraft is typically in closed loop control with thrusters or electrically-powered reaction wheels maintaining or altering the craft's attitude based on sensor measurements.
An example is the Magellan probe that once per orbit interrupted the scanning of the Venus surface making a large turn to direct its high gain antenna to the Earth for data transmission.