Inside the database of a credit reporting agency...

To know what a credit file is you must first understand what a database is and how it functions. A database is structured data that is accessible in a variety of ways. There are about a dozen different kinds of databases, and the credit reporting agencies use one of the most common types, a relational database. At the most basic level, a relational database is an electronic database that arranges information into one or more tables with a unique identifier for each row. In a credit reporting agency's database, each row represents a single consumer while each column contains bits of information attributed to the column header (such as Social Security number or date of birth). 

Two tables found within a credit reporting agency's database are the "name table" and the "trades table". The name table is comprised of columns labeled as "SSN", "First Name", "Last Name", "Date of Birth", etc.... The trades table is comprised of the same information as the name table but also includes columns relating to the "trade" of goods between a consumer and a seller like: furnisher name, lender, account, balance, loan, and so on... The data in the rows are compared to each other through a rigorous procedure to determine if the rows are related. The credit reporting agencies use very sophisticated algorithms to determine if a row in one table is "related" to a row in another table. If the rows are related, they are assigned the same unique identifier and are considered as belonging to the same consumer. In other words, any and all rows across the entire database, regardless of table assignment, that contain your unique identifier, is your credit file.