The Catalog data provides general information about the satellite. This information is very useful when finding Keplerian elements for the satellite. The three common ways of identifying a satellite are by its: (1) Name or ID, (2) 5-digit Catalog Number, or (3) International Designator. The satellite ID is listed below in the table in both abbreviated and full form since it is identified by both somewhat interchangeably. The 5-digit catalog is assigned by NORAD/Space Command sequentially; each satellite has a unique number. The International Designator provides the launch year, followed by the sequential launch number for that year, and a piece identification. The primary piece from a launch (first spacecraft) is traditionally piece "A" and so forth. All payloads are assigned piece identifiers before spent upper stages and other launch debris are assigned identifiers. The piece identifier may be as long as three letters.
You can see pictures of some of the satellites by selecting the Satellite ID links.