Time signatures
explained for drummers.

Longer bars: 6/4 and 8/4

The six above are the common ones, but the top number can be anything. 6/4 is six quarter notes in a bar — count 1 2 3 4 5 6 with the weight on 1 and 4. It shows up in prog rock and in jazz tunes that feel like a stretched waltz.

8/4 is eight quarter notes in a bar. On paper it looks like two bars of 4/4, and you could write it that way — the reason to notate 8/4 instead is phrasing. If the riff, the fill, or the chord change resolves every eight beats rather than every four, one long bar tells the truth about where the music breathes. Gospel, prog, and a lot of instrumental hip-hop sit here.

Anything that isn't 4/4, 3/4, or 2/4 gets loosely called an odd meter — odd time. Strictly it means an odd-numbered top figure (5, 7, 9, 11), but drummers use it for any bar that doesn't divide neatly into four. In DrumShed you can dial any top number from 2 to 13 over a quarter or an eighth, so 6/4, 8/4, 9/8 and 11/8 are all just a spin of the wheel.

Is 4/6 a real time signature?

Almost never — if you've seen "4/6" it is nearly always 6/4 with the numbers the wrong way round. The bottom number names a note value, and note values double: 2 (half), 4 (quarter), 8 (eighth), 16 (sixteenth). There is no note worth "one sixth" of a whole note, so 6 can't sit on the bottom of an ordinary time signature. (Contemporary composers do occasionally write irrational meters like 4/6 on purpose, meaning four beats each a sixth of a whole note — but if you met it in a drum chart or a tab, read it as 6/4.)