Humps usually form around the maturity where the market expects the policy peak. If traders think the fomc hikes for another year and then cuts for several, the 1 to 3 year area prices the highest average rate and the belly of the curve bulges.
Humps are the natural habitat for curve-butterfly trades, where you sell the expensive belly against the wings or the reverse.
Example: 3-month 4.90%, 1-year 5.15%, 3-year 4.60%, 10-year 4.25%, 30-year 4.40%. The hump sits at 1 year, and the 30-year tick up gives the long end a small smile.
Related: curve-butterfly, normal-yield-curve, flat-yield-curve, yield-curve