Karma in Sanskrit means ‘Action’. It is the universal law of cause and effect that dictates that your life is your own making. Goodness reaps goodness and conversely, evil reaps evil. Karma is not just physical actions; in-fact the thoughts we create and the words we speak are Karma too.
In Yogic Science, Karma is considered a glue between the soul and the body. As long as humans have desires and thus associated karma with those desires, they will continue to go through reincarnations (the cycles of life and death) until they have dissolved all their Karmas.
In the endless Karma cycle, at birth, humans are allotted a certain quantity of (Prarabdha) Karma from a repository of (Sanchita) Karma (accumulated Karmas from the soul’s past lives) to be resolved in the current life, however in the process, new (Agami) Karma is accumulated that is added to your total Karma and this endless cycle continues. Perform selfless Karmas that are not binding and hence have the possibility to liberate themselves (achieve Nirvana).
Other reading material: Short answers to real questions about Hinduism
Relevant videos: Swami Nikhilanand Hinduism Q & A: What is Karma?, Hinduism Q & A: What is Good Action, Vikas Gupta, Swami Tadatmananda on Karma,
Contributor: Vikas Gupta
Location of this post (10b): https://www.hinduspeakers.org/ufaqs/what-is-karma/