Fractocumulus a.k.a. Scud
Sunlit fractocumulus makes a stark contrast with the dark cloud base under the flanking line of a supercell in the background. Cumuloform cloud material often gets shredded into ragged chunks in high-shear surroundings like that of a supercell. "Scud" is a popular term, coined by storm observers for decades, for shredded cloud material (fractus) of all types.
1 SE Olney TX (17 May 89) looking SE.