Its your current chivalry rank, hover over the chivalry resource to read more.

Find a shrine to The Lady and go pray at it, it'll give you a buff for +15 Chivalry per day, when the blessing runs out (you can check your blessings in the bottom right menu on the map, click the arrow to expand your resources like morale/troop number/income etc)

Praying at shrines to The Lady will also get you free Battle Pilgrims which are handy in the early game of a Bretonnian Knight run.