“What’s in a name? That which we call a rose by any other name would smell as sweet.” - Juliet, Act II, Scene II
That's a great question Juliet! What is a name? Or word for that matter?
This question is surprisingly difficult to answer for a linguist. There is no single, agreed-upon definition of a word. Every attempt to define what a word is has so many exceptions that it can't possibly be accepted even as a "good enough" definition.
But despite that, we use the word "word" very often, without much difficulty.
In everyday life, the exact definition of what a word is doesn't bother us. It's not super relevant to getting our point across:
"Mother fu----" "HEY! Don't say that word in this house!" "But MOM, what even is a word?"
However, if you're writing a complete guide to learning a foreign language, you're going to end up using the word "word" quite a lot. So having an agreed upon definition, even if rough, helps clear things up.
When we talk about learning words in a foreign language, we're not talking about every single different combination of letters.
By that logic, these would all be different words:
And the word "man" would be considered one word, even with two very different meanings:
The man mans the boat.
So instead we count word families, which are groups of semantically related words.
Eat, eats, ate, eating, eater, eaten, etc. is a single word family and so is good, better, best.