From Computer History Wiki
Structures are a mechanism available in most programming languages for creating a named block of associated data values (usually of mixed types), effectively an extended type; the elements have individual sub-names. Instances of the structure can then be used in various ways - e.g. by being passed as an argument to a procedure.
One common use is to have an array of a particular kind of structure; without structures, the program would have to have N arrays, one for each data item in the structure.