What is a Limitation?

A limitation in your research study is anything you didn't have control over. Here's a quote from Creswell that helps to drive this point home:

Limitations are shortcomings, conditions or influences that cannot be controlled by the researcher. Any limitations that might influence the results should be mentioned. The limitations set forth reservations, qualifications, or weaknesses inherent in the design. Generally, these will reflect anticipated inadequacies in regard to internal validity of results. (Creswell, 2004)

Not to be confused with delimitations!