Terminology for Teacher Pension Form in Taiwan: "基数“ and ”大口“
In the pension form, 基數 means the average monthly salary when he/she applied for retirement. So if the salary was 100 and his/her 個基數 is 56, then the total amount of pension would be 100*56=5600.

For the meaning of 大口, please refer to @thinwa 's interpretation. Just one minor correction, 大口 considers people aged 11 or over.