A hold is a request to reserve a physical library item, such as a book, for a specific person. To put a hold on a book, a person can use the "Request This" feature in IUCAT or call the Service & Information Desk for assistance.
Holdings refers to what a library owns. The holdings section of an IUCAT record can also tell you if a book is available on the shelf, checked out (borrowed) by someone else, or missing.
A web hosting service is when a company or organization that hosts your information on their server so that it can be searched on the internet. You pay to lease (rent) the space on the server from the web hosting service.