Diction simply means word choice. Because poems pack a lot of meaning into a few lines, choosing the right word at each point is terribly important. For example, if you're writing a poem about your dog, what impression is made if, instead of "dog," you call her a pup? puppy? pooch? mutt? doggie? canine?

Overall, a poem may have a formal, elegant diction; there will be no slang. Or it may be informal, with casual wording predominating. Or, of course, it could be somewhere in between, or a combination.

Connotations

But "formal vs. informal" is only the beginning, a general starting point. It's very important to notice the impact of important individual words. Two definitions are useful here:

• denotation is the dictionary definition
• connotations are the emotional and/or intellectual "baggage" a word carries that goes beyond its literal definition. Connotations are common to a culture; they may also be individual to a particular person.

For example: the word "flag"

• denotation: a cloth emblem representing a country
• connotation: patriotism, love of country. Individuals may also associate the flag with battle, political decisions, death (the folded flag given to a soldier's family

The word "mother":

• denotation: female parent
• connotation: nurturing, love, comfort. But individuals might have other associations, e.g. conflict, abuse, high standards.