https://digital.fidelity.com/prgw/digital/finewissues/
A certificate of deposit, or CD, is a federally insured savings deposit that offers a fixed interest rate with the assumption that you will hold your money in that CD until its maturity date. Typically, CDs require a minimum purchase of $1000 and can be opened with multiples of $1000, but with Fidelity's fractional CDs, we allow you to purchase CDs at lower minimums and at increments as low as $100.
Brokered CDs, that is . . . so no compounding of interest
The highest "fractional" rate tonight, through Fidelity, is 5.20% APY for a one-year CD, while, for comparison's sake, they are also brokering a "whole" one-year CD from Chase that yields 5.50% APY
Curiously, they don't say who sponsors that fractional CD.
Perhaps it's Fidelity's own home brew, where they skim off a middleman's (hidden) commission