The novena is an exercise of devotion that is practiced for nine days to obtain some grace or ask for a certain intention.
It can be dedicated to Christ himself in some invocation, or to some canonized saint whose intercession is more powerful before God, due to the merits achieved during his life.
For example the Virgin Mary and the saints. They can be nine consecutive days or nine times on a given weekday (nine Fridays, for example).
In this application you will find a compilation of novenas to pray.