What is the definition of the term "area" in reference to the photon tracked target in the C++ photonlib library?

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In the C++ photonlib library, the term "area" refers to the physical size of the photon tracked target, which is typically represented as a rectangle. The area is usually expressed in terms of its width and height, and is used to calculate various properties of the target, such as its absorption and scattering coefficients, as well as its interaction with other particles in the surrounding medium. The area is an important parameter in photon tracking simulations, as it determines the probability of photon-target interactions and plays a key role in determining the accuracy and reliability of the simulation results.