A consultant is one type of actuary. He works for a consulting firm that is hired by other companies when they need help in such areas as designing a benefit program for their employees, setting up a company pension plan, etc. A consultants work is then billed out to the company using his services. It is a more high pressure, client driven type of work, where the client usually requires the work to be done in a certain amount of time. This often requires very long hours each day (including weekends) as well as some travel (for presentations, etc.), if the client is located in another city.
The other type of actuary usually works in house for an insurance company. The workload usually has less pressure since their are no clients that need to be satisfied. In addition there aren't as many deadlines as opposed to consulting.