The expression that represents the cost of the app for \( m \) months, taking into account a joining fee of $2 and a monthly subscription cost of $5 each month, is:
2 + 5m
This expression accounts for the one-time joining fee of $2 and adds $5 for each of the \( m \) months. Therefore, the correct choice is:
2 + 5m = c (where \( c \) represents the total cost).