Im Anfang Shr Gemaechlich
“To go faster, like you are going slower.” A term used by composers to confuse string sections. Used by the German composer, Gustav Mahler.
Three notes in the space of two, not three in the space of one. For example a triplet over one quarter note is not the same - in that case, it would be written as a triplet over two eighth notes.
Generically, this means a ratio of 3:2. At one point this was used as a description of a perfect fifth since waveforms with that ratio will sound a fifth apart. In recent times, this term has more commonly been used to indicate a rhythm pattern. Formally, it describes a “triplet” or playing three notes in the space normally taken by two. Less formally, it has come to mean playing any rhythm that makes the “feel” different than the notated time signature. For example, playing triplet quarter notes can make 4/4 feel like 6/8 as you would play 4 * 3 / 2 = 6 notes per measure. (Various sources, including https://en.wikipedia.org/wiki/Hemiola.)
The major and minor scales that have the same key signatures but start at different points in the scale. The relative key of any scale is the sixth note in that scale (although may be sharped or flatted). For example, the relative to C major is A minor so: