Concatenation

Concatenation is the process of joining small matrices to make bigger ones. In fact, you made your first matrix by concatenating its individual elements. The pair of square brackets, [], is the concatenation operator.
For an example, start with the 4-by-4 magic square, A, and form
B = [A A+32; A+48 A+16]
The result is an 8-by-8 matrix, obtained by joining the four submatrices.
B =
16 3 2 13 48 35 34 45
5 10 11 8 37 42 43 40
9 6 7 12 41 38 39 44
4 15 14 1 36 47 46 33
64 51 50 61 32 19 18 29
53 58 59 56 21 26 27 24
57 54 55 60 25 22 23 28
52 63 62 49 20 31 30 17

This matrix is halfway to being another magic square. Its elements are a rearrangement of the integers 1:64. Its column sums are the correct value for an 8-by-8 magic square.
sum(B)
ans = 260 260 260 260 260 260 260 260
But its row sums, sum(B')', are not all the same. Further manipulation is necessary to make this a valid 8-by-8 magic square.