Hoarseness is not the same as horse-ness, or even a horse mess, but it can be a mess if you have to sing or talk, but you're hoarse..
What does hoarseness mean? It's a symptom of having swollen vocal cords. A doctor might call it edematous vocal folds, or hoarseness, of course-ness.
It's a good idea to not yell, scream, sing loudly or beyond your trained range because you can smash your vocal folds together too hard (hyper-adduction) and cause irritation from friction. If you're dehydrated, it can happen faster or be worse. If swelling is very bad, you lose the ability to make any sound because mushy vocal folds won't make much sound.
Wait a minute. What is "trained range"? Properly professionally trained singers usually have a lot more range and flexibility than non-trained or badly trained singers.
These same things apply to speaking, so if you use your voice, it's a good idea to take care of it!