...spin1
Historically, the term spin had (and sometimes has) a narrower meaning than angular momentum. Picture an electron in an atom. Sacrificing some accuracy on the altar of visual imagery, think of the electron as orbiting about the nucleus, and spinning on its axis. The orbital motion gives rise to so-called orbital angular momentum; the spinning gives rise to so-called intrinsic or spin angular momentum.

... momentum2
And traditionally stands for orbital angular momentum, and stands for spin angular momentum.

... component.3
People sometimes use instead of to denote this.

... somehow4
Not so trivial, because the three component measurements are mutually incompatible; it is theoretically impossible to measure and simultaneously (for example). Nonetheless, the combination is measurable.

... corrections5
Specifically, Bohr's energy levels agree exactly with those derived from Schrödinger's equation, when we neglect the spin of the electron, the spin of the proton, and relativistic effects. (Spin itself is sometimes considered a relativistic effect.)

... above).6
Sommerfeld gave a single more general quantum condition which implied the quantum conditions for , , and as special cases. So Sommerfeld's approach was not so ad-hoc as this summary makes it look.

... model7
Bohr did not make use of the quantum number ; instead, he had slots at level ( ), each capable of holding electrons. Note that this is actually incorrect.

... vector8
We mean an ordinary 3-space vector, not a vector in a (complex) Hilbert space.

... system9
ignoring any motion of the proton, a good approximation

... publish10
Alfred Landé independently came up with the same half-integer trick. He did publish, and so attached his name to the Landé -factor.

... together).11
These lines are responsible for the color of sodium vapor lamps used on many highways.

... spectrum.12
The sodium D-lines provide an example. The quartet and the higher doublet both have and ; their 's are and .

... small''13
In particular cases, small'' and slowly'' can be given more definite meaning. For example, we may be able to write as a power series in something; might contain the second and higher order terms.