It means number of values in a study that are free to vary. for example, if you have to take ten different courses to graduate, and only ten different courses are offered, then you have nine degrees of freedom. 9 semesters you will be able to choose which class to take; the tenth semester, there will only be one class left to take - there is no choice, if you want to graduate. 

Each of a number of independently variable factors affecting the range of states in which a system may exist, in particular any of the directions in which independent motion can occur. ·    for     CHEMISTRY each of a number of independent factors required to specify a system at equilibrium. ·    for
the number of independent values or quantities which can be assigned to a statistical distribution