Inside the proton are elementary particles called quarks. Quarks and protons have an intrinsic angular momentum called spin. Spin can point in different directions. When it is perpendicular to the proton’s momentum, it is called a transverse spin. Just like the proton carries an electric charge, it also has another fundamental charge called the tensor charge. The tensor charge is the net transverse spin of quarks in a proton with transverse spin.
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Source: Phys.org