NOUNS - DEFINITE ARTICLES VS. INDEFINITE ARTICLES
A definite article refers to a specific item, but an indefinite article
refers to one of something in a class.
the - a sole entity
a - one of several
"I'll have the banana split."
To me, this sentence suggests there is only one banana split on the menu (Bennigan's), and thus no need for further clarification.
"I'll have a banana split."
This sentence could imply that there are several possible banana splits (Bananasplits-r-us): medium, large, exra large, with different combinations of toppings, and thus the person ordering the banana split will need to specify the details.
Or it could just mean that I was staring at Dave the bartender at Bennigan's, imagining the two of us walking on the beach in Cancun past the red flags that warn of danger in the rythymically pounding aqua blue and sea green waves under the bright yellow sunlight, and I used incorrect grammar. The improper use of an indefinite article happens in English all the time. Blame Dave.