1. Open form - These are kind of compound nouns which function as one unique word but are still
written as two or more words separated by the space between them.
Example: 1. Post office / 2. Middle class
2. Closed form - It’s simply two words coming together form a single word without any
Punctuation or spaces.
Example: 1. Baseball / 2. Keyboard
3. Hyphenated word - In this the two or more words are connected through the Hyphen and form
a compound word. Example: 1. Eight-pack / 2. Brother-in-law