Greek letters were widely used in physics, because it is able to make a symbol that has meaning for reading. Just like my previous post about the Alphabet in physics that gives a brief impression in reading. Example of the Greek letter used by the physicists

α (alpha): Acceleration angle.
β (beta), γ (gamma): This type of nuclear radiation, together with α. In special relativity, Lorentz factor γ means.
δ (delta): Dirac delta function.
ε (epsilon): a constant electric permittivity.
η (eta): On several occasions, mean efficiency.
θ (theta): Angle.
κ (kappa): Bulk Modulus.
λ (lambda): Wavelength; meeting the electrical charge per unit length.
μ (mu): magnetic moment. Also used to express the magnetic permeability.
ν (nu): Frequency.
ξ (xi): One type is named with the letter the amount of baryons (Ξ)
π (pi): In addition to the number 3.1415926535 ... is also related to parity symmetry.
ρ (rho): Meeting of the mass or electric charge per unit volume, as well as electrical resistivity (resistor type).
σ (sigma): The electrical conductivity; meeting the electrical charge per unit area. Also to Steve-Boltzmann constant.
τ (tau): Torque.
φ (phi): In a letter size (Φ) means of magnetic flux.
χ (chi): Susceptibility. χe χm to magnets and electricity.
ψ (psi): In quantum physics, is used to express the wave function, which declared a state.
ω (omega): angular velocity. Font size, Ω, for Ohm.