Calvinism is often defended or derided. For freewill theists, Calvinism is the standard foil. But usually there’s not much by way of definition beyond TULIP. Here’s a definition by a great Reformed theologian. It’s a useful point of reference whether or not we completely agree with his interpretation.
It begins, it centers, it ends with the vision of God in His glory…Whoever believes in God; whoever recognizes in the recesses of his soul his utter dependence on God…Perhaps the simplest statement of it is the best: that it lies in a profound apprehension of God in His majesty, with the inevitably accompanying poignant realization of the exact nature of the relation sustained to Him by the creature as such, and particularly by the sinful creature…Theism comes to its rights only in a teleological conception of the universe, which perceives in the entire course of events the orderly outworking of the plan of God, who is the author, preserver, and governor of all things, whose will is consequently the ultimate cause of all. The religious relation attains its purity only when an attitude of absolute dependence on God is not merely temporarily assumed in the act, say, of prayer, but is sustained through all the activities of life…The doctrine of predestination is not the formative principle of Calvinism, the root from which it springs. It is one of its logical consequences, one of the branches which it has inevitably thrown out. It has been firmly embraced and consistently proclaimed by Calvinists because it is an implicate of theism, is directly given in the religious consciousness, and is an absolutely essential element in evangelical religion, without which its central truth of complete dependence upon the free mercy of a saving God can not be maintained.This is the root of Calvinistic soteriology; and it is because this deep sense of human helplessness and this profound consciousness of indebtedness for all that enters into salvation to the free grace of God is the root of its soteriology that to it the doctrine of election becomes the cor cordis of the Gospel. He who knows that it is God who has chosen him and not he who has chosen God, and that he owes his entire salvation in all its processes and in every one of its stages to this choice of God, would be an ingrate indeed if he gave not the glory of his salvation solely to the inexplicable elective love of God. B. B. Warfield, “Calvinism,” The New Schaff-Herzog Encyclopedia of Religious Knowledge.