What are coherent and incoherent radiation?

I am a mathematician who is self-learning physics. In reading Jackson's electrodynamics and other books, I often hear that radiation is incoherent or coherent. What does this mean? Does it just mean that the phases are the same in coherent radiation and is different in incoherent radiation?

What are coherent and incoherent radiation?

I am a mathematician who is self-learning physics. In reading Jackson's electrodynamics and other books, I often hear that radiation is incoherent or coherent. What does this mean? Does it just mean that the phases are the same in coherent radiation and are different in incoherent radiation?

I am a mathematician who is self-learning physics. In reading Jackson's electrodynamics and other books, I often hear that a sum is incoherent or coherent. What does this mean? Does it just mean that the phase is the sum in coherent sums and is different in incoherent sums?

What are coherent and incoherent radiation?

I am a mathematician who is self-learning physics. In reading Jackson's electrodynamics and other books, I often hear that radiation is incoherent or coherent. What does this mean? Does it just mean that the phases are the same in coherent radiation and is different in incoherent radiation?