The answer is emulsions. Milady classifies shampoos directly: shampoos are oil-in-water emulsions with a pH range of 4.5 to 7.5.
The book adds that because shampoos don't contain the harsh alkalis found in soaps and detergents, they leave hair in a more manageable condition. Creams, solvents, and ointments are all real product categories used elsewhere in barbering, but the specific chemistry classification the book gives shampoos is emulsion.
Milady Standard Barbering, 6th ed., Ch. 11 (Treatment of the Hair and Scalp), p. 277: "Shampoos are oil-in-water emulsions with a pH range of 4.5 to 7.5."
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