3 (or 4) consecutive gracenotes (g¹, a¹ and g¹), executed by the little finger, sometimes extended with a preceding Singling; Naturally, the starting and target notes are identical (a¹); Examples taken from Logan:

1: starting a¹ - g¹-a¹-g¹ - target a¹ (often executed as 2: a¹-g¹-a¹-g¹ - target a¹), and 3: if preceded by a Singling: g²-a¹-g¹-a¹-g¹ - target a¹.
NB: Example(s) to be replaced with staff-notation.