Record sequential files are nearly always referred to simply as sequential files because when you create a file and specify the organization as sequential, a record sequential file is created by default.
To define a file as record sequential, specify ORGANIZATION IS RECORD SEQUENTIAL in the SELECT clause for the file in your COBOL program, for example:
select recseq assign to "recseq.dat" organization is record sequential.
Because record sequential is the default for sequential files, you don't need to specify ORGANIZATION IS RECORD SEQUENTIAL. As long as you do not set the SEQUENTIAL Compiler directive, you can simply use ORGANIZATION IS SEQUENTIAL.