Rather than dividing thoughts into classes like "good" and "bad," Buddhist thinkers prefer to regard them as "skillful" versus "unskillful." An unskilled thought is one connected with greed, hatred, or delusion. These are the thoughts that the mind easily builds into obsessions. They are unskillful in the sense that they lead you away from Liberation. Skillful thoughts, on the other hand, are those connected with generosity, compassion and wisdom. They are skillful in that they may be used as specific remedies for unskillful thoughts, and thus can assist you toward Liberation.
-Henepola Gunaratana, Mindfullness in Plain English