A multiword font name is a font family name which contains white space. For example:

For best results enclose such font names in quotes in your attached style sheet. Commas and semicolons should be outside the quotes.

The following font family names contain one word each and need not be enclosed in quotes:

body {font-family: "Courier New", Courier, mono;}
H1 {font-family: "Times New Roman", Times, serif;}

You may enclose all font family names in quotes if you prefer.

body {font-family: "Courier New", "Courier", "mono";}
H1 {font-family: "Times New Roman", "Times", "serif";}