A more thorough explanation:

A Markush claim is a type of patent claim that includes a list of alternative chemicals, materials, or steps in a process. The alternatives must all give the same result, rather than patentably distinct products. The name comes from Ex parte Markush, 1925 Dec. Comm'r Pat. 126.

• A patent claim for a new type of paint that includes a list of alternative pigments, such as "selected from the group consisting of red, blue, and green."
• A patent claim for a new type of drug that includes a list of alternative chemical compounds, such as "selected from the group consisting of compound A, compound B, and compound C."

These examples illustrate how a Markush claim allows for flexibility in the materials or chemicals used to achieve the same result. The claim covers all the alternatives listed, as long as they produce the same outcome.