Find lengths of quadrilateral sides:
,
,
,
.
Since all sides have the same lengths, you can state that this quadrilateral is rhombus.
Let's check whether quadrilateral JKLM is a square. To check this let find the lengths of diagonals:

,

.
The lengths are different, so quadrilateral is not a square.
Answer: quadrilateral JKLM is a rhombus.