Is trajectory the same as an orbit? Is trajectory the same as an orbit?
I wanted to know about gravity assists, but most books I find are talking about different types of orbits and such.
Are they related?
 A: The terms trajectory and orbit both refer to the path of a body in space. Trajectory is commonly used in connection with projectiles and is often associated with paths of limited extent, i. e., paths having clearly identified initial and end points. Orbit is commonly used in connection with natural bodies (planets, moons, etc.) and is often associated with paths that are more or less indefinitely extended or of a repetitive character, like the orbit of the Moon around the Earth.
I did had an exact question few months back, but this page from NASA provided good amount of information regarding trajectory and orbit. 
A: Nop!
The definition of an tridimensional trajectory, is the set of 3D points $(x(t), y(t), z(t))$ determinted by the parameter $t$. Which means, it's a function $\mathbf r(t)$, where $\mathbf r: \mathbb{R}\mapsto\mathbb{R}^3$. Of course we can generalize to the $n$-dimensional case: $\mathbf r: \mathbb{R}\mapsto\mathbb{R}^n$, where $\mathbf r(t) = (x_1(t), x_2(t), ..., x_n(t))$. The parameter $t$ often is the time, but it shouldn't be restricted to that.
The definition of an orbit caused by a central force, is a trajectory expressed by the function: $\phi(r)$. Where $r$ is the distance which connects both objects and $\phi$ is the polar angle.
Notice: In an orbit, the function implies the motion is periodic, and limited to a plan. This is not a limitation since, in all central forces, the angular momentum of the system is conserved, which implies the movement is restricted to a plan, perpendicular to the direction of the angular momentum.
A: 
Is trajectory the same as an orbit?

Yes and no. For example, you will see many textbooks and papers use the term hyperbolic orbit. I use the term myself. On the other hand, the ballistic part of a weapon's flight from the gun (or missile silo) is called a ballistic trajectory rather than a ballistic orbit.
A: An orbit is a special case of a trajectory. Any ballistic flight path is a trajectory (throwing a ball or firing a cannon) and an orbit is a special case where the trajectory does not intersect the locally dominant gravitational body - at least in the short term.
