This is a classic. The one word that we all probably learn after “dad” and “mom”, the most basic way of greeting there is in any language, and the easiest way of asserting “I know how to say something in another language”.
When we translate “Hello” to Spanish, something curious happens:
Hello in Spanish is “Hola”, In English there’s “hello” and “hi”, the first is “formal”, the sort of polite word you use when talking to anyone, including people you don’t know, whilst “hi” is more friendly and this implies that it wouldn’t be a good idea to say hi to everyone, especially when it’s someone we just met, worse if it’s an old person: It just feels impolite, even if the person doesn’t take it personal.
In Spanish we say “Hola” to everyone, you can say “Hola” to a friend, family, an old person or a stranger.
This is one of the very few exceptions in the more common non-written rule which states that in Spanish everything is harder than in English.