Please can you give me a detailed description of mailshot?

The term mailshot is not one you are required to know for Standard Grade computing. You may however be asked for some of the details associated with sending out a bulk personalised mailing to a large group of recipients. This process involves creating a standard letter, inserting fields from a database for personal details of customers etc., merging the two together to create personalised copies of the standard letter. This process is called a mailmerge.