Most Physics degrees require multiple lab courses to graduate. As a rule of thumb, the more labs you have to take for your Physics degree the better. Your Senior Lab is the culmination of your degree. It is the most technically demanding lab course you have taken as it involves working in groups to set up experiments, perform the experiments, analyze the results and present them in written form and often as a presentation. This is all done largely independently and should be taken seriously.
Senior Lab is typically a two part course taken over the whole of your senior year. Some schools allow you to substitute the second part with research under a professor. At schools that allow this substitution the professor does not have to be a physics professor. If it is approved it can be in any department so long as the work is appropriate. The requirements to take the course are to of course be a senior but to have completed most of the Junior course work and to be enrolled in the Senior courses. Many of the experiments require knowledge of Electricity and Magnetism, Quantum Mechanics, and Thermal Physics.
There is only one course option for the actual Senior Lab. However, performing research under a professor before getting to this point should be a high priority for every student. It not only will likely prepare you for taking this course, but it will also help to fill out your resume with something akin to job experience. research is the next best thing a student can do after an internship.