Field research involves the independent variable being manipulated in a natural environment, is valid and authentic, but lacks mundane realism as participants cannot consent to the experiment.
Natural research lacks control over the independent variable as it would happen anyway, can be done under highly controlled conditions in a lab, and allows research that wouldn't normally get done to be done.
Quasi research involves an independent variable that is based on existing differences, has high external validity, high demand characteristics, and low internal validity.
Pilot study is a small scale trial run of the investigation to ensure there are no problems with the research later on, saving money and time in the long run.