Martha Katz's- what is it before a noun?

When the noun "Martha Katz's" is placed before a noun, it indicates that the noun belongs to Martha Katz.

The apostrophe s ('s) at the end of her name is a possessive form. Something in the sentence belongs to her.

Examples:

Martha Katz's house is on Maple Street.

I made the cake with Martha Katz's recipe.

This classroom is Martha Katz's.