Rhytm is used by external plugins, the metronome, modulators, and jack transport.
Here are some other common names for the term "signature": time signature, meter signature, meter, metre, measure, and measure signature.
Example 1: If tempo is set to 64 BPM, and the signature is set to 8/8, a new bar will be played every 16 seconds (64/4 * 8/8), and a new beat will be played every 2 seconds (64/4 * 1/8). Example 2: If the signature is set to 2/4, a new bar will be played every 8 seconds (64/4 * 2/4), and a new beat will be played every 4 seconds (64/4 * 1/4).
To show the Signature track, right-click somewhere in the timing area of the editor (to the left of the note tracks), and enable "Signature".
Signature format: u/l. (u = upper numeral, l = lower numeral)