What Is The Kingdom?

The Kingdom of God is the whole territory under the rulership and dominion of God (Yehovah);
(The whole Universe, and all that's in it.)
Also, commonly referred to as "The Kingdom of Heaven".

The Kingdom of God is best summed up in this parable:


The parable of the wheat and the tares:
“The kingdom of heaven is like a man who sowed good seed in his field. But while his men were sleeping, his enemy came and sowed weeds among the wheat, and left. And when the wheat sprouted and produced grain, then the weeds also became evident. And the workers of the landowner came and said to him, ‘Sir, did you not sow good seed in your field? How then does it have weeds?’ And he said to them, ‘An enemy has done this!’ The workers said to him, ‘Do you want us, then, to go and gather them up?’ But he said, ‘No; while you are gathering up the weeds, you may uproot the wheat with them.
Allow both to grow together until the harvest; and at the time of the harvest I will say to the reapers, “First gather up the weeds and bind them in bundles to burn them; but gather the wheat into my barn.” ’
Matthew 13:24-30

You can read further at:
Understanding the Kingdom