A field is an area in a fixed or known location in a unit of data such as a record, message header, or computer instruction that has a purpose and usually a fixed size. In some contexts, a field can be subdivided into smaller fields. Here are some examples:
1) In a database table, a field is a data structure for a single piece of data. Fields are organized into records, which contain all the information within the table relevant to a specific entity. For example, in a table called customer contact information, telephone number would likely be a field in a row that would also contain other fields such as street address and city. The records make up the table rows and the fields make up the columns.
2) In a form that you fill out on a Web site, each box that asks you for information is a text entry field.
3) In the header of a variable-length transmission unit, a two-byte subfield in the header (which is really a field itself) could identify the length in bytes of the message.