Note: there are also indefinite articles, we can't forget that.
When something is defined, it is also, in every sense of the word, definite.
Using a definite article allows the reader to understand which particular moose you are referring to: The blue moose, the moose in front of you, the moose from Texas that you almost killed with your car. The moose is defined. To say,
the moose means you and the reader know which moose is being spoken of/written about.
Jonathan was overwhelmed by the moose with boxing gloves.
Shiela resorted to poking the moose with a stick.
We definitely know which moose overwhelmed Jonathan, just like we definitely know which moose Shiela decided to start poking.
Using an indefinite article allows the reader to understand that you're just referring to the general object and also that there may or may not be more of them.
A blue moose doesn't necessarily mean there is only one moose that is blue, just like
A dead moose doesn't mean that all moose are dead, but rather, there is at least one.
For Halloween, Jason dressed up like a moose.
Every Christmas, my brother and I receive an egg with a chocolate moose in it.
Before we knew it, a moose entered the room.
We do not exactly know which moose Jason dressed up as, or which chocolate moose is in the egg, nor do we know which moose entered the room.
Though, once it has entered the room, people will refer to it as
Then there is just the use of the word. In this case, there is no need to mark the noun as defined or not defined, because it is just an object now. It's there in the sentence to act as just that, an object.
We eat moose
Taylor leaves tomorrow morning to hunt moose.
In some cases, it can be an indirect object
Tim wears a sporty jacket made from moose.
I know this entire answer and all examples are in English, but the same rules apply to Spanish usage and distinction between a definite and indefinite article. Anyway, I'll provide a Spanish snippet if it makes everyone happy.
Maria come pastel
Maria come un pastel
Maria come el pastel
The same rules from my English examples above apply here. The first sentence simply implies that Maria eats cake, and that's all we know. In the second sentence, Maria eats a cake. This suggests there is more than or at least one cake being eaten, The first sentence defines a cake, a particular cake. The cake on the table; the cake next to the cheese; the cake made with bacon.