The capital stock of any bank or financial institution that could be subject to assessment. Assessable capital stock makes shareholders liable for an amount greater than what they paid for their stock. However, the assessment of this stock only takes place in the event of bankruptcy or insolvency.
Any capital stock that can be called and is not fully paid for can technically be referred to as assessable capital stock. However, the term is generally reserved for stock of banks or other financial institutions. Obviously, assessment of this stock will usually lead to a loss for the shareholders.