A Planet's dignity basically refers to the strength of its position in the chart. A Planet is strong, or said to be Dignified, when in a sign that it rules: (See chart Signs of the Zodiac: Houses and Planetary Rulers.) It is said to be exalted when in specific signs, or to be in its fall or detriment when in other certain signs. The origins of the principles are lost in antiquity, and thought by some astrologers to be obsolete. This is beyond what we want to study now, but it helps to understand the terms when they appear in something you are reading.