To understand what a yeoman was it is really necessary to undertand the English feudal system. Nobody owned their own land outright in the Middle Ages except the King and a few of the Nobility and even they had to pay some sort of service in return for their land. Gradually the Nobility began to let some lesser people have their own land in return for service such as military service or providing other services. By about the 14th century land could be awarded by the Lord of the local manor to local farmers. In a way they owned it but they still had to pay a token service to the Lord. It could be pased on to their heirs but only with the permission of the Manor Court. This was known as "copyhold." Very few farms were "freehold": these farmers were the original yeomen not aristocracy but they definitely considered themselves a cut above the ordinary manorial tenant. Fortunately for us researchers, most of them left wills. If you kknow that you have a yeoman ancestor in England look for a will. As time went by the feudal system died out, people were able to buy land, and men who only rented large farms called themselves yeomen. It depends on the time frame that you are looking at and also part of England that you are looking at as to what "yeoman" meant. Some areas changed faster than others.