Transferable skills refer to skills you may have learned through previous work experience, education, volunteer experience or other activities in your life which can be transferred and are useful for a range of different jobs. An example could be that you like video games, well some skills involved there are making quick decisions, thinking strategically, using leadership abilities in some cases, all these skills could be transferable to any number of jobs. Or let's say you volunteered with children, this kind of work involves a lot of communication, patience, decision making and quick thinking, again—all very transferable skills. It's important to know, what your transferable skills are, and take time to consider then before you apply for a job.
It's also a good idea to put common transferable skills on your resume. And when you are in an interview, always try to talk about other jobs in detail to convince them of your skill set and talk about specific moments where you had to use a skill that is needed for the new job you are applying for.