Karma is a consequence visited upon you due primarily to your thoughts, feelings, words and actions.
Each of these is an energetic force and produces a reaction. Thoughts and feelings are powerful, and they can produce a physical effect on your body. Others can feel your vibration as well. Your spoken words and actions are powerful in that they generate a reaction in those around you.
Karmic residue can be accumulated lifetime after lifetime if the issues are not dealt with and resolved, thus its resolution is postponed.
You might have different types of karma but one lifetime may not be sufficient in resolving all of it. Perhaps it involves a deceased person who needs to be in your life again. Perhaps it involves you being younger, thus rebirth would be required.
Karma is as natural and basic to universal life as the laws of physics. There is no way to avoid karma or bypass it. You may not be aware of karma, but it is certainly aware of you and keeps you involved in facing the consequences of your thoughts, utterances, feelings, and actions.
Sometimes the consequences seem minor and thus do not alert you sufficiently to cause you to make changes. However, this does not negate the fact that you will have to deal with it down the road, if not in this lifetime.
Karma is neutral. It is the ultimate equalizer in that it does not discriminate nor is it random.
What karma are you aware of in your life right now?