Within the subfield of international relations, and political science as a whole, the concept high politics covers all matters that are vital to the very survival of the state: namely national and international security concerns. It is often used in opposition to "low politics".
Although the idea of high politics has been present in all cultures and epochs, Hobbes was the first to enunciate that survival (of trade, the laws, societal order, etc.) hinges upon a finite number of ingredients. For him, these ingredients were embodied and provided by the State. However, interpreting Hobbes, these ingredients are what we call "high politics."
The term "high politics" in itself was probably coined during the Cold War, given the stakes of an atomic war. The advent of the atomic bomb made it clear what was ultimately worth fighting for and what was not. Hence, made clear what "high politics" meant. In that sense, the United States and the former USSR would have gone to war for a direct atomic threat (see Cuban Missile Crisis), but would have never gone to war over "low politics", say, a boycott of the Olympic games (see 1980 Summer Olympics). Trade, for all its importance, is considered by most political scientists as "low politics", as it depends on specific security conditions to come into effect.