@[columnname] and tablename@[columnname] are used for structured referencing in excel tables.

Features of structured referencing:

1- If in the formula, there is at least one structured referencing from inside of the table, the column is autofilled.

2- It is more convenient to have column name rather than a alphabetic column headers.

3- If a new row is added to the table, the column already created using structured referencing, gets updated.

4- If you start typing the columnname, it is autosuggested by excel

D2 =[@Wage]/B2 is an structured referencing the column is autoexpanded:

E3 = C3-C2 is structured referencing and the column is auto expanded.

If Mohammad (age=39, wage = 36000) is added, the other columns are autoexpanded: