The "erase-remove idiom" refers to a common programming error where a developer mistakenly uses the functions erase and remove interchangeably. While both are used to delete elements, they operate differently. The erase function is typically used to remove elements from a container, like a vector or list, while remove shifts elements to effectively "remove" them but does not change the container's size. This idiom can lead to confusion and bugs in code. For instance, using remove on a vector may leave unwanted elements in the container, requiring a subsequent call to erase to actually reduce its size. Understanding the distinction is crucial for effective programming.