The term "a priori" refers to knowledge or reasoning that is independent of experience. It is often used in philosophy to describe concepts or truths that can be understood through logic and deduction rather than through empirical observation. For example, mathematical truths, such as 2 + 2 = 4, are considered a priori because they can be known without needing to measure or observe anything in the physical world. In contrast, "a posteriori" knowledge is based on experience and observation. For instance, knowing that water boils at 100 degrees Celsius requires empirical testing. Understanding the difference between a priori and a posteriori helps clarify how we acquire knowledge and the foundations of various fields, including philosophy and science.