Worth keeping in mind that these ideologies each have multiple self-definitions (the ideal with which they describe themselves) as well as a set of definitions from the perspective of each other ideology. Tack on semantic drift (words changing meaning over time, or growing different meanings in different contexts) and it can start to feel hopelessly complicated. And they each offer different ways of understanding the world and history, so on top of all the aforementioned complexity, they also interpret historical events and real-world applications of each ideology differently. So learning about them is a process where your understanding slowly moves from abstract to concrete by getting rough definitions then tempering them with seemingly contradictory definitions, over time building a network of understanding that includes the contexts of each perspective.
My perspective is largely coming from a communist ideology fyi. But here’s a quick rundown.
Capitalism is a system in which a class of owners leverage their ownership of productive assets to engage in non-equal exchange with the un-owning classes, most notably the exchange of labor value for a fraction of the products of said labor value. It necessitates a large government to enforce these hierarchies of ownership and exclusion. (Classical) liberalism is the ideology of capitalism. Conservatism is generally a subset of liberalism. It’s the culturally dominant ideology now, so most of what you see and read will come from this perspective, explicitly or not.
Communism is a theoretical system in which class tensions have resolved themselves. No one knows what it’ll look like, it’s explicitly a theoretical ideal. Communism as an ideology is advocating for the interests of the working class against the owning class. A country that calls itself communist would probably be doing so in reference to the ideology, rather than claiming it has achieved communism.
Socialism as an ideology can be synonymous with communism, although there are subsets of liberalism that have taken on the word to mean capitalism with welfare and regulations. Socialism as a system is the interim stage between capitalism and communism, the point where workers have seized control of the state and means of production and now have a strong influence over how class tensions develop.
Tankie is an empty signifier
That is to say, it’s a label that can be used to describe an array of different and conflicting ideas, values, and identities. Because of this it serves as an obfuscatory device rather than a communicative one. The sub-logic becomes tankie = bad, so if someone I don’t like = tankie, then person I don’t like = bad.
Almost none of us were alive when Khrushchev rolled tanks into Hungary. Most MLs aren’t particularly fond of Khrushchev.
It’s made a resurgence in this new, weird context because most of the terms used during the previous red scares lost their power through similar misuse. It’s become unfashionable to hate on leftism in progressive spaces, doing so using old terminology makes you sound like a fox news conservative. But you can do the same thing by calling it this instead.