As already mentioned by Steeven, escape velocity is the minimum velocity required for an object to forever move away from some body (to escape the body's gravitational field). It can mathematically be described by
$$v_{esc}=\sqrt{\frac{2GM}{r}}$$
where $G$ is the Gravitational constant, $M$ the body's mass and $r$ the distance to the center of the body. It should however be mentioned that escape velocity is only needed if there is no external force acting on the "escaping" body. This means that if you reach $v_{esc}$ for an infinitesimal short amount of time, you would escape the Earth's (or any other object's) gravitational field.
If, on the other hand, you keep accelerating or there is a constant force acting on you, you don't need to reach escape velocity. For example, this is the case with rockets which constantly burn engine - they don't reach escape velocity during takeoff.
On a side note, orbital velocity can be described by
$$v=\sqrt{\frac{GM}{r}}$$
(As mentioned by notovny, this formula only holds for circular orbits).