In the early text of the
Theravada Buddhism, Kamma basically means action which is said to refer to both
wholesome and unwholesome-KUSALA and unwholesome AKUSALA actions. It is also called
the law of cause and effect because wholesome action produces good result and
unwholesome action leads to serious consequence respectively.
According to Buddhist perspective, all actions are not Kamma unless they are accompanied by intention or volition. It means that all volitional actions generate Kamma, so that the Buddha said, in the Majjhima-nikaya," O! Bhikkhu monks, it is volition - cetana that I call Kamma, -cetanaham bhikkhave kammam vadami, having willed one acts through body - kaya kamma, speech - vaci kamma, or mind - mano kamma.
In Buddhism, kamma has two aspects, namely , kammic activities - kammabhava and kammic results - kammavipaka. Having confused kammic results with kammic actions, people often complain that their difficulties and suffering or Dukkha in this life are due to their past kamma because it is very closely related to the doctrine of rebirth. However Lord Buddha rejected the belief that all human experience in this life is determined by their past kamma - sabbam pubbekatahetu, or the view determined by the will of a supreme God - issaranimmanna-hetu.
The Buddha went further to explain that, in the Samyutta-nikaya1, p 227, Yadisam vapate bijam tadisan harate phalam; kalyanakari kalyanam papakari ca papakam. It amounts to saying "one reaps what one sows; the doer of good receives good, the doer of evil receives evil. "However , one who pays for his or her bad kamma no longer becomes an obstacle. In the early history of Buddhism, let me bring out one of the evidences that Thera Angulimala who becomes an arahat by overcoming all his bad kamma. In the Dhammapada V.127, it also states that "whoever by good deeds covers the evil done, such a person illumines his or her world like the moon freed from clouds."
However, according to the functions of kamma, there are four kinds , namely,  productive kamma - janaka,  supportive kamma - upatthambhaka,  obstructive kamma - upapalaka, and destructive kamma - upaghataka. These four apply to both wholesome and unwholesome kamma . The major effect of productive kamma is to give birth according to the commentator's standard view. But in other views , it could produce results in the course of existence -pavatta vipaka. The other three effect the kammas both in kusala and akusala in the course of existence, in supporting , obstructing and destroying the kammas.
In Buddhism, there are the five kammas which are considered most heinous; (1) killing one's own mother, (2) killing one's own father, (3) killing an arahat, (4) wounding the Buddha and (5) causing a split among the community of Buddhist monks, known as 'apayika narayika parikuppa atekiccha'. It means that if one has committed one of these five most serious kammas, there is no other realm to escape or hide from the serious consequences .These five kammas are called Pancanantariya kamma in the sense they bear result definitely in the next life. In accordance with the concept of obstructive kamma, the view - kamma-avarana, that kamma becomes an obstruction for liberation in that very life [Anguttara-nikaya III .p 436], if one has committed one of these kammas, it will obstruct his or her ultimate goal to attain Nibbana within that particular birth, but he or she is not obstructed forever. According to the Culakammavibhanga-sutta in the Majiihima-nikaya III, p 202, the youth, named Subha, asks the following question from the Buddha:-
Master, Gotama, what is the reason , what is the condition, why inferiority and superiority are met with among human beings, among mankind? For one meets short-lived and long-lived persons, sick and healthy persons, ugly and beautiful persons, insignificant and influential persons, poor and rich persons, low-born and high born persons, stupid and wise persons. To this, the Buddha answered in the following manner: Student, beings are owners of kamma, heirs of kamma, they have kamma as their homing place. It is kamma that differentiates beings according to inferiority and superiority.
Although the exact mechanism of kamma is unpredictable, Buddhism has no doubt about the fact that kamma is responsible for one's birth in a particular existence and the desirable quality of life, one acquires at one's birth.