Well...not always.
A rocket is a projectile or missile that is powered by a rocket engine. Palin and simple, whether guided or not. A rocket engine gets its thrust from propellants that are carried within the body of the rocket itself, put there before use (like a fuel that is mixed with an oxidizer and then ignited to form thrust). Most rockets generally use solid fuels because they are easier to maintain and can be deployed faster, although large ballistic missiles do use liquid fuel rockets. So, sometimes rockets are guided, and when they are, they are usually also referred to as missiles.
Generally, missiles are either rocket propelled (like an Intercontinental Ballistic Missile (ICBM)) or use something other than a rocket for propulsion, like a jet engine. Generally, when people talk about a missile, they are speaking of a guided missile that uses some form of a jet engine. This is usually a turbojet because they are relatively easy to build and maintain. But turbofans and ramjets are other common engines used in missiles.
Hope that helps.
There is crossover with missiles, but all rockets use a rocket engine. If it does not...then it is not a rocket. A guided missiles can also be a rocket if it uses a rocket engine, but most people refer to jet powered guided missiles when talking about missiles these days.
