A dipole magnet is an electromagnet used in particle accelerators to create a homogeneous magnetic field over some distance. Particle motion in that field will be circular in a plane perpendicular to the field and collinear to the direction of particle motion and free in the direction orthogonal to it. Thus, a particle injected into a dipole magnet will travel on a circular or helical trajectory. By adding several dipole sections on the same plane, the bending radial effect of the beam increases.
In accelerator physics, dipole magnets are used to realize bends in the design trajectory (or 'orbit') of the particles, as in circular accelerators.