The "P" of PM may refer to product, project, or program. Make sure to check which type of PM the firm is specifying in the job description!
Product Management
Product managers oversee the entire lifecycle of a product, from introduction to growth to maturity to decline. The product manager is responsible for the success of the product across these phases. The task is never considered complete, since the consumer landscape is always changing.
Project Management
Project managers are in charge of a project with specific start/end dates and defined objectives. The project manager must develop the goals for the project, determine the workflow, and manage those working towards the common goal.
Program Management
Program managers work with multiple different projects that are interconnected in order to achieve bigger picture goals. In contrast with projects, programs do not have a definitive timeframe and are focused on strategy rather than a tangible outcome.