The best one word definition of a need is a deficiency. In the homeostatic sense, needs are created whenever there is a physiological or psychological imbalance.
With a few exceptions drives or motives are set up to alleviate needs. A drive can be simply defined a deficiency with direction. Drives are action oriented and provide an energizing thrust toward goal accomplishment. They are at the very heart of the motivational process. The examples of the needs for food and water are translated into the hunger and thirst drives for affiliation.
At the end of the motivation cycle is the goal. A goal in the motivation cycle can be defined as anything which will alleviate a need and reduce a drive. Thus attaining a goal will tend to restore physical or psychological balance and will reduce or cut off the drive. Eating food, drinking water and obtaining friends will tend to restore the homeostatic balance and reduce the corresponding drivers. Food water and friends are the goals in this example.