Maybe this is a question that should be asked at english.se in stead. I am just wondering if you can talk about "going through customs", when referring to all processes involved in entering/transferring a country. Or are the terms just as synonymous as Consulates and Embassies?
They are different. The reason people use the terms interchangeably is that at many border crossings (especially at airports) one set of people handle both.
Customs is about the stuff you are bringing into the country. Is it allowed, should you pay duty, should it be confiscated and burned, etc. By default, none of your stuff is allowed in, even if you're a citizen returning home.
Immigration is about a person who is visiting, immigrating, or returning home. By default visitors are (technically) turned away unless they have a good reason and meet other criteria (for example visitors to Canada may be turned away if they have a criminal record) and those who live here are let in. Immigrants are let in if the paperwork they've done in advance is all correct.
Both processes involve "who are you, where are you coming from, why are you coming here, why were you there" and so on. Both involve a uniformed person, your passport, and probably your baggage. For example if you say you are visiting for 3 days, but you have brought weeks worth of clothing - probably all you own - along with more permanent possessions like books, photo albums, and CDs, an immigration officer may suspect you are moving here. Customs officers may want to inspect your baggage for contraband, and your explanation for your visit may make the difference between being inspected or not. As a result they are considered a single process in most people's minds.
To add to the complication, many airlines won't let you board unless you convince them you will be let in at your destination, and some airports (especially in Europe) want to look at your passport and other immigration-related documentation several times before you get to the boarding gate. None of this counts as "clearing customs and immigration" but it may sure feel like it.