Technically, abstract means an idea that is general and not based on particular examples. It is also a brief summary of a research article which helps the reader quickly ascertain the paper's purpose.
The term abstract refers to a concept or an idea that is not associated with any specific instance. This term can also be used to refer to a vague summary of the main points of an argument or theory.
An abstract is basically a summary of all the main points of the article. It is usually a paragraph in length. But sometimes can be made longer, to be helpful for people who have little time to read the article and want to know all the main points in short, concise paragraph.