The most common vore practitioner, prey characters live to be eaten and/or engulfed. 

The motivations for prey differ from person to person, but the Endosomatophilia aspect is often an important one.  Feeling warm wet flesh all around them is a very sensual experience to imagine, stimulating to every bit of their body.  The desire to be conquered by someone bigger, stronger, or just hungrier than the prey is also common. 

People playing as prey may cross the line into weight-gain, willingly sacrificing their bodies to a predator in order to make them fatter.  Fat predators are alluring to some because not only are they obviously very successful at catching/luring prey, the fat on their bodies is a manifestation of the many lives snuffed out in their guts.  Touching their flab is touching flesh that used to belong to others.

Just like sex, prey have a preference for what gender their predator is.  This choice usually aligns with their sexual preference, but not always.  Some prey prefer not to engage in blatantly sexual play during vore scenes, while others happily hump tongues and throats on the way down to the waiting stomach.

Some prey enjoy banter from their predator, being mocked over their weakness or praised as a fine fat meal that will nourish the predator for days to come.  Others prefer to be treated with all the regard we would give a potato chip.  It is food, nothing to be spoken to, mocked or praised.  Some prey even want non-sentient predators who may not even be aware they're devouring a sentient creature.

There are grades of willing and unwilling attitudes in prey.  They range from diving gleefully into a pred's mouth to fighting tooth and nail for their life.  In between are those who allow themselves to be tricked and eaten, offering token resistance, and prey who allow themselves to be swallowed but escape digestion through means of their own or the predator's.  Digestion used to be a matter of course for many vorarephiles, but as the pool of vore fetishists online grew, other attitudes and preferences arose.

[There are as of yet no authoritative publications from academics on the subject of vore as we know it, only on the loosely-related subject of cannibalism, so I rely on my identity as a vore fetishist for over a decade, author of many erotic vore stories, and frequent vore-scene roleplayer to lend authority to my definitions.]