Men's fashion is filled with confusing terms, making it unclear to many when to wear what type of pant. Khakis play a role in this confusion, especially in an age when dark denim jeans are often considered appropriate in certain semi-formal settings. The term "dress pant" is generic, with multiple sub-categories of trousers potentially fulfilling the definition. Understanding the difference between terms helps to look appropriate in any situation.
Slacks
Slacks are technically any pant you could wear with a jacket or in business casual environments. Slacks are typically dress pants that are not part of a suit, featuring a generic fit. Slacks are pleated or flat-front, come in multiple colors and are made of linen, cotton and lightweight wool. Slacks, in accordance with their name, are usually not as trim-fitting as one might prefer with a tailored suit.
Chinos
Chinos are very similar to khakis in many ways. Usually light tan or beige, chinos also refer to a lightweight khaki-style pant available in multiple colors. The term pertains more to the weight of the fabric than any other styling detail. Chinos are typically flat-front versus pleated and have a smooth finish.
Corduroys
Corduroy pants are often considered slightly dressier alternatives to jeans, but casual nonetheless. Corduroy pants are defined by their ridges, with varying wale thicknesses -- some approaching velvet-like smoothness. However, cords are still outside of the "dress pant" category, but perfectly acceptable with a blazer in certain less formal circumstances.
Khakis
Khakis are a trouser type, as well as the color that usually describes their appearance. Khakis, like chinos, are normally a tan or beige tone. The pant is a slightly heavier weight than a pair of otherwise similar chinos. Khakis may be pleated or flat-front, and like corduroys, are acceptable with a blazer versus a true suit jacket.