What is "semicomma"

The semicomma, also Fokker's comma (after 31-TET pioneer Adriaan Fokker), is type of small musical interval, or comma, in microtonal music equivalent to 2109375:2097152, or 3 ⋅ 5 : 2. This is a ratio of approximately 1:1.0058283805847168, or about 10.06 cents . It is derived from the difference in pitch between three 75/64 just augmented seconds and one 8/5 just minor sixth begun on the same root ((3 × 274.58) - (1 × 813.69) = 823.74 - 813.69 = 10.05 cents).