What operation is this in maths

Question

I need to develop an algorithm for a problem then translate it into code, but I am sure someone would had done it before, my question is that what is the name of operation in below sudo code ?

var a = [1];  // or it can be x1
var b = [1,2]; // or it can be  y1,y2

var c = a operation b;
console.log(c);

Output:    [1.1, 1.2]; // or  11,12   // [x1, y1], [x1, y2]

Output will be combination of a x b so formula would be, a + (each elment of b set)

is it union or interaction or nothing like this exists ?

Update

1,2,3 are properties of Arrays. Decimal is only added for explaining my problem.

Here is the real problem I am trying to solve https://stackoverflow.com/questions/37571034/merge-tree-of-tables-into-a-single-flat-table