Plain English Meaning
This is the name of a specific ILS approach plate for Runway 28. When more than one ILS approach exists to the same runway, each one gets a letter (Y, Z, X, and so on) so pilots can tell them apart and brief the correct one.
Full Definition
An instrument approach chart title indicating one of multiple Instrument Landing System (ILS) approach procedures to Runway 28 at a given airport. The letter 'Y' is an alphabetical suffix used to distinguish this ILS procedure from other ILS approaches to the same runway (such as ILS Z RWY 28), where each version differs in some operational element — for example, transition routes, minimums, missed approach procedure, or required equipment.