1. Spaced or Open Compound Noun : is one in which there is a space between the two words which form the compound noun. For example: Cricket bat / Fast food / Flower shop
2. Hyphenated Compound Nouns : is one in which the two words are separated with the use of a hyphen. For example: By-product / Mother-in-law / Passer-by
3. Closed or Solid Compound Nouns : is one in which the two words do not have any spaces or hyphens separating them. They are usually considered as a single word.
For example: Sunflower / Classroom / Rainfall