To gain access to a single element within the array, a subscript is used. A subscript may be a numeric constant or an integer-valued variable, is enclosed in parentheses which identify the position of a given element in the array. For example, the first element of array TEST (containing the value 15) is referred to as TEST(0J. The second test score is as TEST[1], the third test score is as TEST[2], and so on. Therefore, the following statements are true:

TEST[0] = 15
TEST[1] = 25
TEST[2] = 5
TEST[3] = 81
TEST[4] = 75
Here, 0, 1, 2, 3 and 4 within parentheses are known as a subscript.

Subscripts are numbers that come after a symbol and below. 

For your reference: A_3, B₃ etc.