Karma is a basic law of material nature through which the supreme authority and power of the Supreme Personality of Godhead is expressed. Karma means that one gets a reaction for any activity that is performed within the material world, in other words, it refers to the law of action and consequent reaction.

The Bhagavad-gita describes three types of karma, whereas “karma” in these explanations is understood as action.

1. Karma: Pious activities in accordance with the higher laws of nature or the Vedic scriptures. This type of action generally allows the living entity to reach higher planets after leaving the present body or at least get another human body on earth.

Some of these activities are: giving donations to brahmanas, building of hospitals or wells, feeding hungry people, or any other helpful and generally beneficial activities. One has to understand, however, that it is impossible to completely avoid sinful activities since one already kills countless tiny life forms simply by breathing.

2. Vikarma: Illicit activities against the laws of nature. Each activity which ignores or opposes the Vedic injunctions or their basic activities can be considered to be in that category.

Within this category of activities are: the torturing and killing of animals, theft, cheating, intoxication, arson, illicit sex-life, prostitution and similar activities which destroy the social harmony and peace in society.

The consequences of vikarma are e.g. birth in a low class human life form under suffering and miserable conditions, poverty, incurable and severe diseases, or birth in a non-human life form.

As the activities of the living entities are never exclusively pious or sinful and the law of karma is very subtle and extremely complex, it is impossible to give an extensive description which goes beyond the basic principles.

One may achieve a high position because of one’s good karma, but since it is practically impossible to completely avoid sinful activities and one may also have to expect sinful reactions from previous lives. One can suddenly fall from one’s high position and be forced to reap one’s bad karma.

Though the good and bad reactions to our previous activities are unavoidable and unchangeable for a karmi (fruititive, motivated worker), one still has the free will to change one’s course of action in every moment of one’s life. If the action however, is already performed, one has to either enjoy or suffer the reactions for it. The reactions for our activities don’t have to necessarily be experienced within our present life but can also be manifest in our next life. This explains e.g. unnatural conditions by birth. The accumulation of gross actions in our present life influences our subtle body at the time of death and thus we create our next body.
3. Akarma: The effect of the law of karma can only be avoided by transcendentalists who are engaged in akarma-activities. Activities which don’t cause karmic reactions are known as “akarma”. This does not refer to material inertia by not doing anything. Purely transcendental activities which are performed solely for the pleasure of the Supreme Personality of Godhead are akarma.(Bhagavad Gita 3.9)

This type of activity qualifies us to reach the spiritual world after leaving our present body.

One should, however, note that it is impossible to perform akarma-activities without being guided by an experienced spiritual master. The reason for this is that we are not able to fully understand the desire and plan of the Lord. In other words, akarma means that one acts beyond self imposed conceptions of “good” and “bad”.

“A person who accepts the path of devotional service is not bereft of the results derived from studying the Vedas, performing austere sacrifices, giving charity or pursuing philosophical and fruititive activities. Simply by performing devotional service, he attains all these, and at the end he reaches the supreme eternal abode.” (Bhagavad Gita 8.28)
One cannot refrain from action. One’s actions need to be purified and at the same time one should not be attached to the results. Here is Lord Krishna’s instruction:

“Whatever you do, whatever you eat, whatever you offer or give away, and whatever austerities you perform-do that, O son of Kunti, as an offering to Me. In this way you will be freed from bondage to work and its auspicious and inauspicious results. With your mind fixed on Me in this principle of renunciation, you will be liberated and come to Me.” Bhagavad-gita 9.27-28