While I've never had a problem discerning between rulings and houserules in previous editions, as most games don't rely on DM opinion so much, I find that 5th edition is problematic regarding this terminology. The game gives the DM great leeway to interpret the rules and the game, and provides no written alternative to giving an opinion-based ruling in many situations. It also provides the DM with multiple options for how to represent things, which are treated as being within the intent of the game. With all of this going on, I keep on hearing people refer to regular situational rulings as being houserules… But houserules are generally a replacement or extension of the core rules, not just an interpretation of what to do in a given situation. Are people just using the word houserule wrong, or does 5e force DMs to invent houserules left-right-and-center?
In other games which are very strongly dependent on individual interpretations, abstract reasoning, and situational rulings, people almost never call a GM's decision a "houserule" unless they're actually changing something about the mechanics. But in 5e, I've encountered people saying that everything from a simple yes/no answer to a question, up to representing the damage of falling ship spars with the rock fall trap are all house rules! Is this just people used to more strict rules systems having difficulty understanding the concept of a DM ruling?
noun: ruling; plural noun: rulings
1. an authoritative decision or pronouncement, especially one made by a judge.
1.currently exercising authority or influence.
House Rule's official definition is very loose and variable between sources. Generally it refers to a rule which applies only to a set group of people in a set place or situation. However, it still specifies that a house rule must be a "rule", meaning it would include the definition of rule.
1. one of a set of explicit or understood regulations or principles governing conduct within a particular activity or sphere.
Remember Good Subjective, Bad Subjective and answer with more backing than just your own personal opinion please.