Although the word "prodigal" does not appear in the Bible, the Parable of the Prodigal Son is known by many who do not believe the Bible is the Word of God. In fact, Buddhism has a similar teaching found in their sacred writings (Saddharmapundarika Sutra 4). The Chinese call their version of the prodigal son 敗家仔 (Mandarin: Pinyin; Cantonese: Bai ga jai), which means "Son Ruining the Family." The story has been the subject of movies, paintings, songs, and of course, many books.
Webster's New World Dictionary defines "prodigal" to mean "extremely wasteful." That definition partially describes the younger son in Luke's Gospel (15:11-32), but he apparently had many more flaws in his character than that. He was impatient, wanting his inheritance before his father died. He was morally bankrupt in that he spent his wealth on "riotous living" (v. 12), or more bluntly, on prostitutes (v. 30). He, himself, described his lifestyle as sin against heaven and in his father's sight (v. 21). In other words, I believe he recognized his disrespectful treatment of his father ("in thy sight"), as being, perhaps in his repentant condition, worse than the sins in a "far country" (v. 13).
Based upon Webster's definition, the natural tendency is to view the younger son as the subject of the tragic story, but I would suggest to you that his older brother may have been a greater prodigal. Notice his reaction to hearing of his brother's return and the response of his father (v. 27-30). He had been faithfully working in the field, and as he was returning home, he heard the celebration. He was angry, and would not go in, but notice what his father did. Unlike he had done when his younger son was not a part of the family, he went out to reason with his elder son (v. 28). The "faithful son" was upset that he had spent his life serving his father, and living a moral life, only to be taken for granted (v. 29). In his own mind, he saw himself as a prodigal in that he apparently had wasted his life for nothing.
Even though the meaning of this parable seems obvious, it should not be understood as an isolated teaching. It follows the Parable of the Lost Sheep, where the shepherd leaves 99% of his flock to focus upon locating the one which is lost (v. 3-7). In that parable, the shepherd goes after the lost sheep, but in the case of the prodigal, he waits for the lost one to return on his own. In the Parable of the Lost Coin, the woman frantically searches until she finds her lost coin (v. 8-10). From these three parables, I believe God reacts differently because the sheep, coins, and men picture different levels of understanding of their relationship to Him. The sheep know He is their Shepherd, but don't know how to get to Him. The coin doesn't know it is lost, so He takes it upon Himself to "find" it. The prodigal knows his Father loves him, but in his rebellion, he chooses to reject Him; it is up to him to find his way back home. In other words, God only does what is necessary for us to be with Him, but in every case, He does enough so that we are without excuse on the day of judgment (Creation - Rom. 1:20; Commandments - Gal. 3:24; Cross - Eph. 2:16). He is faithful; the question is, are we?