* - A (Astronomical), N (Nautical), C (Civil)

+ - twilight refers to the dull light that can be seen near the horizon even though the Sun is yet to rise or has set already
Astronmical twilight refers to the moment when sun is about 18^o below the horizon. This usually is taken as the time when Sahr ends (and Fajr begins) in the mornings and as the beginning of Isha in the evenings
Nautical twilight refers to the moment when sun is about 12^o below the horizon. The morning light at this time has been historically taken to be enough for navigational purposes
Civil twilight refers to the moment when sun is about 6^o below the horizon. The light at this time is usually taken by civic authorities in many countries to be the time to turn off the street lights, head lights of vehicles etc

Transit refers to the time in which the Sun reach its highest point in its east-west movement everyday. Luhr begins shortly thereafter