The Fortran data statement is a means of initiating values in a variable. For example the statement below assigns the value 3.7 to the variable x.
real :: x data x/3.7/
It is a very handy method of initializing arrays:
integer, dimension(10) :: aray data aray/1,2,3,4,5,6,7,8,9,10/
There is nothing inherently wrong with the data statement, but it can easily be replaced with an array initializing statement of the form:
aray = (/1,2,3,4,5,6,7,8,9,10/)
It is not inherently a legacy feature though.