In the Western world, music wise, we split an octave into 12 equal parts - now called 12EDO, or equal temperament.
We also split (usually) an octave into what probably sounds like seven 'equal' parts. We call those major and minor scales.
Obviously, with 12 divisions on one hand, and 7 on the other, there's going to be trouble. In a key/scale of 7 notes, each must have a separate letter name, otherwise writing them on manuscript would be horribly messy.
So, we use letter names A to G, then start again.Unless we are German, and bring H into the equation, making it all more interesting!
Now, using the 7 letter names, only once each, there are going to be musical gaps between each on either a semitone (one step/fret) or a tone (two steps/frets).
Developing over many centuries, we now have A>B=T, B>C=S, C>D=T, D>E=T, E>F=S, F>G=T, G>A=T. When keys other than the ubiquitous C major are used, some of those notes need to be sharpened or flattened in order to sound in tune.
In the case of, say, Eb major, the spacing of the notes need the E to be flat, and also A and B. So it ends up having 3 flat notes in that key.
Another well used layout is the keyboard, where the white keys are called ordinary (natural) notes, A>G, and the black keys get called sharps OR flats, depending on the key of the prevailing piece.
Don't know where the terms 'step and half-step' come from, but they're universally known as tone (T) and semitone (S). They're sometimes portrayed as W (whole) and H (half), which seem to correspond to your terms better.