A file consists of a sequence of records. In a text file a record corresponds to a line of text; in other cases a record has no physical basis, it is just a convenient collection of values chosen to suit the application. There is no need for a record to correspond to a disc sector or a tape block. READ and WRITE statements always start work at the beginning of a record and always transfer a whole number of records.
The rules of Fortran set no upper limit to the length of a record but, in practice, each operating system may do so. This may be different for different forms of record.