What Is Karana?
A tithi is the time the Moon takes to pull 12 degrees ahead of the Sun. Karana is half of that, just 6 degrees.
So each tithi has two karanas. A lunar month has 30 tithis and 60 karanas. On most days you'll see two or three of them.
Karana is one of the five limbs of the Panchangam: tithi, vara, nakshatra, yoga and karana.