This document defines 25 key research terms used across various research methods including surveys, focus groups, case studies, experiments, observations, content analysis, ethnography, action research, grounded theory, historical research, Delphi technique, meta-analysis, longitudinal studies, correlational studies, quasi-experiments, randomized controlled trials, cross-sectional studies, case-control studies, cohort studies, simulations, research questions, hypotheses, variables, sampling, and data analysis.