Role overload occurs when an individual experiences excessive role demands. 

Quantitative overload is when role expectations mean there is too much to do.

 Qualitative overload is when the individual does not have the experience or ability to carry out role demands.

 Having more than one demanding role at the same time, like parent and professional, or a job position with many weighty responsibilities, are frequently researched examples (Marks, 1977). 

Role underload is the opposite condition in which the individual has very few role demands, or the demands are very easily accomplished. Underload may also be quantitative or qualitative.

 Both overload and underload are job stressors. They, in conjunction with other job stressors and the amount of control individuals feel they have over job demands, have been found to be predictive of stress related illness. Death from overwork (“karoshi”) in Japan or burnout are commonly used examples of the negative consequences of overload. The relationship of overload and underload to variables like absenteeism, job satisfaction, and accidents is inconsistent, probably being affected by other moderating variables. Time management techniques are used to deal with problems of quantitative overload.
Read more:

http://psychology.iresearchnet.com/industrial-organizational-psychology/job-satisfaction/role-overload-and-underload/
http://www.sciencedirect.com/science/article/pii/0030507370900425