What is the difference between a Panel Study and a Cohort Study? I am having a special subject named "Methodologies of Scientific Research" in which there is a reference on Panel Studies and Cohort Studies for conducting a longitudinal survey. I am confused to what is the difference between Panel Study and Cohort Study ? In Wikipedia they look the same, that is Panel Study redirects to Cohort Study.

Edit: My field is related to Computer Science and more specifically Information Technology in an undergraduate level. The subject "Methodologies of Scientific Research" though is not constrained on applications on IT, rather it is more general and we have research examples from other sciences like Sociology, Biology, Economics etc.
The terminology for longitudinal research designs differs somewhat between disciplines. However, to my knowledge most discipline refer to a "cohort" as an entity that can be distinguished by a certain event as for example the year of birth or graduation from high school. The general idea is that there is an observable variable for the cohort membership and that individuals from the same "cohort" have something in common, e.g. the risk to die from lung cancer due to a common time of exposure. Thus, a "cohort study" looks at one cohort or compares different cohorts. In most cases, cohort studies use longitudinal research designs, but there are also cross-sectional cohort studies.
The use of the term "panel study" seems to me more vague but a "panel study" is in most cases a longitudinal study which has at least observations from two points in time. Panel studies do not need to focus on cohorts. 
Hence, cohort and panel studies both look specifically at the timing of certain events and variables. 

For further information you could for example have a look at the following articles in the International Encyclopedia of the Social &amp; Behavioral Sciences:


Mason, W.M. and Wolfinger, N.H. 2001: Cohort Analysis, in:
International Encyclopedia of the Social &amp; Behavioral Sciences,
edited by N.J. Smelser and P.B. Baltes, Pergamon, Oxford, pp.
2189-2194. 
Duncan, G.J. 2001: Panel Surveys: Uses and Applications,
in: International Encyclopedia of the Social &amp; Behavioral Sciences,
edited by N.J. Smelser and P.B. Baltes, Pergamon, Oxford, pp.
11009-11015.