Overview
Gravity is the force, initially described as a force by Isaac Newton, which pulls massive object together. It is responsible for that observation that objects fall to the earth.
Gravitational Field
As a calculation device, one can define a vector field called the gravitational field, which is defined as
{% \vec{g}(\vec{r}) = \vec{F}/m %}
which then implies that
{% \vec{g}(\vec{r}) = - \sum_{i=1}^N \frac{G m_i}{r_i^2} \vec{e}_i %}