Column name with square brackets

[#1]

I have seen some scripts adding  square brackets "[]" after the column name. What does that mean?

example : there column name is shopID

script : Loc = Num(Words(1, :shopid[]));

[#2]

That can be used to access value(s) of the column depending a bit where it is being used. Usually I use (or rather I don't as I prerfer using [Row()]) to access value of current row

Names Default To Here(1); 

dt = open("$SAMPLE_DATA/Big Class.jmp");

/*
Show(row());
show(:name[]); // will fail as current row is 0 (non-valid)
*/

Row() = 1;
show(:name[]);
show(:name[Row()]);
show(:name[1]);

Row() = 28;
show(:name[]);
show(:name[Row()]);
show(:name[28]);

Scripting Guide > Data Tables > Access Data Values > Set or Get Values by Column Name 

Access Cell Values through Column References