Final answer:
The word 'service' in the provided sentence is a noun, which is a word that refers to a person, place, thing, or idea.
Step-by-step explanation:
From the sentence provided, 'Service' is the noun you are asking about. In English, a noun is a word that refers to a person, place, thing, or idea. In the context of the sentence 'I am very happy with the service I received today,' 'service' is the thing that you received, making it a noun. Other examples of nouns include 'mother,' 'father,' 'sister,' and 'teacher,' as mentioned in the reference information provided.