It is important to include definition of terms in your thesis or dissertation in order to understand the key terms being used in the study. These terms should be clearly defined according how they are used in the study in order to make easy understanding of the problem and avoid ambiguous meaning to terms which can be otherwise interpreted in different ways.
Terms defined should be arranged in alphabetical order and acronyms should always spell out fully most specially if it is used for the first time and not commonly known.
Make sure to define though common may have special meaning or used differently. Complicated and lengthy definition should be included in your appendix.