They are known as hidden arguments. Since the LAPACK and BLAS functions are Fortran functions that take some character arguments, the Fortran convention is to pass the length of the character arrays in the arguments as arguments at the end of the function.
Take the DGEBAK function for instance. It has two arguments JOB and SIDE that are single-length character arrays (so a single character). Therefore, we include two arguments that are just 1 after the info argument to say that the JOB and SIDE arguments are only of length 1.