Karma, in general, refers to the reaction of one’s activity. Essentially the same principle of “You reap what you sow”.
Firstly, we will take a look at what different religious scriptures have to say about karma.
In the Bhagavad Gita (14.4), Krishna or God tells his dear friend Arjuna that "In every living entity, there is a spirit soul," and hence by killing any living entity, we gain bad karma.
In the Quran (17.13), it is mentioned that Allah is always watching us and he holds us responsible for our bad deeds and our good deeds.
In the Bible (Galatians 6:7), it is mentioned "Do not be deceived: God is not mocked, for whatever one sows, that will he also reap."
In this way, all religions accept the principle of Karma, something that is important in understanding why we need to be vegetarian.
Just like a country runs under a set of certain laws made by the government, this whole world runs under the laws of material nature. When we kill innocent animals, we bind ourselves to the karma for that action and will receive an equal and opposite reaction. Eating a vegetarian diet is one of the main ways we can avoid karma.