Halflings are often thought of as "half" humans. Clever name right? In other fantasty worlds, you may think of Hobbits. They are very similar in stature and personality. So if you like to think of them as Hobbits, go ahead. The only thing missing is halflings do wear shoes and don't have hairy feet.
But in all seriousness, they are very weak, have very low endurance, and are very fragile/delicate. What they do have going for them is extremely high agility initiative, and speed (to dodge attacks), as well as high dexterity and charisma. They also have very high creativity. As you might imagine, they make excellent bards, thieves, rogues, ninjas, etc.
Finally, they are very resistance to slowness effects and ensnaring. The best way to deal with them is to hit them with an area of effect spell/attack so they can't put that high dodge to good use!