Karma is action, the cause and effect of what we do.  According to the classical scriptures from India, there are four types of karma:

-Sanchita Karma: This is basically all-inclusive karma.  It is what we have accumulated from previous lifetimes, and past actions in this lifetime, good and bad.  It is everything we need to work out eventually – now or later.

-Prarabdha Karma: This is the karma that we are working off in this lifetime.  Since we choose our birthtime, we also choose the planets that are there at the time of our birth, which affects our karma. 

-Agami Karma: This is the more immediate kind of karma.  When we do something and see the effects right then and there.

-Kriyamana Karma: This is how our purposeful actions affect our future karmic return.  If we are more aware of the actions we take, and act out of kindness we will be able to improve our future karma.