An can be described simply as a summary of the contents of a book, article, or speech. However, an is often more complex than this with a variety of information included such as the scope, purpose, methodology, results, and conclusions of the research, all written very concisely. This is not designed as an evaluation of the work, but instead as a description to summarise the work to readers who have not yet read the whole piece of work.
You may wonder why researchers bother to write abstracts. Abstracts can help potential readers to get a brief understanding of a piece of work that allows them to decide whether or not they will read it, and this is important to researchers with limited time. As well as this, they often contain key words from a piece of weird and this helps to index works, therefore making them easier to categorise and find. When researchers are searching for work that focuses on certain topics, they will often search online databases that search that abstracts. This means that the of a piece of work is vital for making it easy to find.