These are different font families, at least as far as CSS is concerned.

Note that if the font name includes spaces, you need to wrap it in quotes:

font-family: Arial;
 
font-family: "Arial Black";
 
font-family: "Arial Narrow";

At least as far as CSS is concerned, these are different font families.

Note that if the font name includes spaces, you need to wrap it in quotes:

font-family: Arial;
font-family: "Arial Black";
font-family: "Arial Narrow";

You can choose the bold or italic fonts in a family like this:

font-family: Arial;
font-weight: bold;
font-style: italic;

If a family doesn't contain bold/italic/bold-italic fonts, they'll be simulated by distorting the base font. This should be avoided, as it doesn't usually look good.