Depending on how long your work is, you story will be considered be a different name. This is not a definitive list, different sources will move the word count here and there. This is just a way to classify length, and you can say short story or novel to make it easier, but in case you're wondering, here is the list:
Drabble: A drabble is around 100 words. But you can tell a story for less. There is a story about Hemmingway who won a bet in a bar when he was challenged to write a story in six words (This is known now as a six-word story). He wrote "For sale: baby shoes, never worn." That sentence said more than some novels do. Drabbles are good if you have an idea you want to get out but don't have the environment or characters to expand on it. This length is good for a quick post on steemit if you have an idea but can't take it further.
Flash Fiction: This is what I write a lot of on steemit. It is considered flash if it is under a 1,000 words but that is a good length for a social media site. There are other terms like dribble for 50 and sudden fiction for 750, but I like flash as an umbrella term. You can get out an idea, a character or two, and even explore a section of a world in that length. You don't want to flesh out too much in that small space but for a quick tale or an interesting idea, this is a good length.
Short Story: This is the normal length that many people are familiar with. A story that is less than 7,500 is considered a short. Shorts are long enough to let you explore a world and a character but short enough that the writer must keep it clean. Short stories can be as deep as a novel and Alice Munroe, who won the nobel prize for writing, exclusively wrote shorts. This is also a good length for people writing posts on this site as it gives them the space to tell a great story and is still digestable.
Novelette: This is another term term that you don't hear often. People usually just use novella but anything that is 7,500 to 17,500 is technically a novelette. For this length as long as novella, I find they just happen naturally when you are telling a story. Sometimes a character or an event needs more room and you find yourself here. I think you should let the story be whatever length it is going to be and if that happens to be a novelette, then so be it.
Novella: Anything that is 17,500 to 40,000 is a novella. If you are trying to publish your work, it might be in your interest to make it a novel but if the story only needs so many words, then for quality, it is better to make it a novella. This, as with novelette, is an odd length for a steemit post but could be broken into pieces.
Novel: The standard measure of a story. A novel has to be over 40,000 words. That is the cut-off. This is for a full exploration of characters, worlds and events. If you are going to post a novel into your steemit account, you should do so with chapters or pieces.