Cursor (round)
A pointer ("curseur") that jumps to a fresh HMAC result once a game has burned through the 32 bytes of one hash.
Each HMAC-SHA256 call hands you 32 bytes. Split into 4-byte chunks, you get 8 floats. Dice and limbo only need one. But plinko with 16 rows, mines with lots of mines, or card games need more than 8.
How it works
The usual message ends with a round number: clientSeed:nonce:round. You start reading bytes from round 0. Once that's used up, the game computes another HMAC using round 1, moves to round 2 if it still needs more, and keeps going. The cursor (curseur) just tracks your spot in that byte stream. Depending on the site's docs, you'll see it called cursor, round or current round.
Why you should care
Check a 16-row plinko ball against a single HMAC and you'll get rows 1 to 8 right and everything after that wrong. Any decent verification tool moves through the rounds automatically.
Example
Say a mines bet uses 24 floats. That's 96 bytes, so you need three HMAC outputs: round 0, round 1 and round 2, at 32 bytes each. The floats get read in order across all three.