The covetous man is ever in want.
-- Horace (65 BC - 8 BC), Epistles
The Sanskrit word steya means "to steal." Asteya is it's opposite: non-stealing or non-covetousness. The root meaning, and the karmic meaning, is simply, "Not taking anything that hasn't been given freely."
In the teachings of the Yoga Sutras, Asteya is the third of the five Yamas, or abstentions. It is identical to the eighth of the Biblical Ten Commandments, "Thou Shalt Not Steal."
Asteya applies, of course, to the material world and our common concepts of stealing: armed robbery, shoplifting, auto theft and muggings. In exactly the same way, asteya also cautions against taking your neighbor's newspaper, bringing pens and thumbtacks home from the office, or any of the myriad "minor thefts" that we commit, often by inventing our own justice or justification.
But asteya, just like all of the Yamas, has a deeper meaning.
Asteya also means honoring another person's trust in us. If someone entrusts you with something, or shares something with you in confidence, you cannot take advantage of him or her.
The karma, or action, of asteya also means developing consideration for how we ask for another's time and attention. If, through inconsiderate behavior, we demand another's attention when not freely given, this is also stealing.