The label of associate professor typically refers to a professor who is tenured. Associate professor is an intermediate rank, between assistant and full professors. The associate professor participates in the three sets of duties that come with a career in academia: teaching, research, and service like all other professors. All professors do more than teach classes; they also must conduct scholarly work, specifically, present and publish their work in peer reviewed conferences and journals. The third set of duties that come with the job of being a professor is service. Service duties entail all of the administrative work that keeps a college or university running. Service includes sitting on committees ranging from creating and evaluating curricula to overseeing workplace safety. Associate professors are often expected to become more active and take on more leadership roles as they become more senior members of the university. Given that they have earned tenure and cannot be dismissed without due cause, associate professors conduct the service tasks that junior faculty members cannot, such as evaluating other professors for tenure and promotion. Some professors remain in the associate rank for the rest of their careers. Others seek promotion to the highest academic rank: professor. 

Associate and adjunct professor

There are lots of different titles that your professors might have:assistant professor, associate professor, professor emeritus, and even just plain professor. However, amidst all of these titles, is likely something that stands out: adjunct professor. So just what are adjunct professors? And how are their roles unique at your college or university? Perhaps the key distinction of an adjunct professor is that he or she is a part-time professor at your school. An adjunct may teach one class for one semester and then never appear again; conversely, he or she may teach one or two classes for several years.  However, adjunct professors are, in many ways, used to supplement the course offerings at an institution by definition. They are not considered full members of the faculty even though they are teaching courses. It should be noted, however, that a professor's status as an adjunct has nothing to do with the quality of his or her teaching.  If, say, you were in a class taught by a full-time professor on your campus, having  an adjunct teach your class or facilitate a seminar does not mean you will be getting anything less than you would have. Some adjuncts are great and others could use some improvement just like tenured professors. Their status as adjuncts does not imply that their teaching skills are less (or easier) than anyone else at your school. Consequently, you should treat and interact with adjunct professors the same as you do the other faculty -- and, hopefully, staff -- on your campus: respectfully and courteously. Someone's status as an adjunct doesn't prevent them from giving you a failing grade or writing you a letter of recommendation or a providing you with a professional introduction down the road if applicable. There are much more other important things about associate and adjunct professor.