The Alt Right is of the political right in both the American and the European sense of the term. Socialists are not Alt Right. Progressives are not Alt Right. Liberals are not Alt Right. Communists, Marxists, Marxians, cultural Marxists, and neocons are not Alt Right.
The Alt Right is an ALTERNATIVE to the mainstream conservative movement in the USA that is nominally encapsulated by Russel Kirk's 10 Conservative Principles, but in reality has devolved towards progressivism. It is also an alternative to libertarianism.
The Alt Right is not a defensive attitude and rejects the concept of noble and principled defeat. It is a forward-thinking philosophy of offense, in every sense of that term. The Alt Right believes in victory through persistence and remaining in harmony with science, reality, cultural tradition, and the lessons of history.
The Alt Right believes Western civilization is the pinnacle of human achievement and supports its three foundational pillars: Christianity, the European nations, and the Rule of Law.
The Alt Right is openly and avowedly nationalist. It supports all nationalisms and the right of all nations to exist, homogeneous and unadulterated by foreign invasion and immigration.
The Alt Right is anti-globalist. It opposes all groups who work for globalist ideals or globalist objectives.
The Alt Right is anti-equalitarian. It rejects the idea of equality for the same reason it rejects the ideas of unicorns and leprechauns, noting that human equality does not exist in any observable scientific, legal, material, intellectual, sexual, or spiritual form.
The Alt Right is scientodific. It presumptively accepts the current conclusions of the scientific method (scientody), while understanding a) these conclusions are liable to future revision, b) that scientistry is susceptible to corruption, and c) that the so-called scientific consensus is not based on scientody, but democracy, and is therefore intrinsically unscientific.
The Alt Right believes identity > culture > politics.
The Alt Right is opposed to the rule or domination of any native ethnic group by another, particularly in the sovereign homelands of the dominated peoples. The Alt Right is opposed to any non-native ethnic group obtaining excessive influence in any society through nepotism, tribalism, or any other means.
The Alt Right understands that diversity + proximity = war.
The Alt Right doesn't care what you think of it.
The Alt Right rejects international free trade and the free movement of peoples that free trade requires. The benefits of intranational free trade is not evidence for the benefits of international free trade.
The Alt Right believes we must secure the existence of white people and a future for white children.
The Alt Right does not believe in the general supremacy of any race, nation, people, or sub-species. Every race, nation, people, and human sub-species has its own unique strengths and weaknesses, and possesses the sovereign right to dwell unmolested in the native culture it prefers.
The Alt Right is a philosophy that values peace among the various nations of the world and opposes wars to impose the values of one nation upon another as well as efforts to exterminate individual nations through war, genocide, immigration, or genetic assimilation.

TL;DR: The Alt Right is a Western ideology that believes in science, history, reality, and the right of a genetic nation to exist and govern itself in its own interests.

The patron saint of conservatives, Russell Kirk, wrote: "The great line of demarcation in modern politics, Eric Voegelin used to point out, is not a division between liberals on one side and totalitarians on the other. No, on one side of that line are all those men and women who fancy that the temporal order is the only order, and that material needs are their only needs, and that they may do as they like with the human patrimony. On the other side of that line are all those people who recognize an enduring moral order in the universe, a constant human nature, and high duties toward the order spiritual and the order temporal."

This is no longer true, assuming it ever was. The great line of demarcation in modern politics is now a division between men and women who believe that they are ultimately defined by their momentary opinions and those who believe they are ultimately defined by their genetic heritage. The Alt Right understands that the former will always lose to the latter in the end, because the former is subject to change.