The h with the bar is the reduced Plank's Constant, i.e., Planck's Constant divided by 2π, which is the quantum of angular momentum.
The | 〉is Dirac notation, also called Ket notation, and indicates a state vector.
Note that in physics, a vector is not just an abstract mathematical entity. It expresses something physical, usually in terms of three dimensional space.
The whole expression is the unit by which the angular momentum of electrons (usually) is described. A given electron in an orbital in the electron shell of an atom has an angular momentum in multiples of the expression. Since Planck's constant is quantized, this is why there are discrete orbitals in the electron shell of an atom, which is why chemistry exists.
