Lord refers to the Graha that owns this nakshatra. As there are nine Grahas and 27 nakshatras. Each Graha owns 3 nakshatras. As is very well known to all Jyotish students, the 27 nakshatras form the basis of the Vimshottari Dasha system. Maharshi Parashara holds this Dasha system to be the most powerful tool for predicting future trends and events in the life of a person. The sequence in which the nine Grahas rule the 27 nakshatras determines the sequence of the Mahadashas, Antardashas, Pratyantardashas etc. in the life of the person.
The system further implies that the position of Chandra in a certain nakshatra at birth determines that the first Mahadasha in the life of the native is ruled by the Graha that owns the Janma nakshatra. The second period will be ruled by the lord of the next nakshatra, and so on. The figure in brackets behind the Graha indicates the length of its Mahadasha in terms of full years.
Note that the sequence of the Navagrahas (nine planets) repeats itself three times in the same fixed order. Maharshi Parashara provides a certain shloka which is helpful in memorizing the sequence of the Navagraha (Chapter 46, verse 12):
which stands for:
Aditya (Surya), Chandra, Kuja (Mangal), Rahu, Guru, Shani, Budha, Ketu, Shukra.
The lord of the Janma nakshatra plays an important
role in the whole life of the person.
Note that each series of nine nakshatras covers one third or 120° of the Kalapurusha. This means that nakshatras that are posited 120° from each other share the same Graha as their lord. The starting point of each of the three series of nine nakshatras coincides with the starting point of the three fire Rashis, i.e. Mesha, Simha, Dhanu.