Usage is the way words, phrases, or things are actually used in practice. When your English teacher talks about proper usage, she means using words correctly in sentences: knowing that “fewer” goes with countable things like cookies while “less” goes with uncountable things like water, or understanding that “literally” shouldn't be used when you mean “figuratively.”

The word can apply beyond language too. A phone's battery usage describes how much power different apps consume. A library tracks the usage of its computers to know when they're busiest. Water usage measures how much water a household consumes.

In language, usage matters because words can be technically correct but still sound wrong or awkward. You might say “amongst” is correct English, but current American usage strongly prefers “among.” Usage changes over time: Shakespeare used “you” differently than we do today. Some words that were once considered errors, like “contact” as a verb, became acceptable through widespread usage.

Good writers pay attention to usage because it affects how natural and clear their writing sounds. A usage guide is a reference book that explains these kinds of distinctions. When someone has “good usage,” it means they choose words that fit the situation and sound natural to educated readers and listeners.