Many HP printers feature letters after the model number.  For instance, the HP LaserJet Pro 4201 comes in 2 variations: 4201dn and 4201dw. If you are a buyer looking for a new HP printer for your home or office, these extra letters may be confusing, but they help to describe some of the main features of their particular models.

Here is a list of many common model variations and what the letter represent:

• d – duplexing
• n – networking
• t – extra paper tray
• dn – duplex and networking
• dtn – duplex, networking and extra paper tray
• dw – duplex and wireless
• x – duplex, networking and extra paper tray (many older models have the "dtn" variation, but that has been replaced on more current models by the letter "x")
• xh – duplex, networking, extra paper tray and hard drive
• xm – duplex, networking, extra paper tray and mailbox
• xs – duplex, networking, extra paper tray and stacker
• xsk – duplex, networking, extra paper tray, stacker and stapler
• sk – stapler and stacker
• f – fax
• h – hard drive
• i – card slots
• w – wireless
• wf – wireless and fax
• bt – Bluetooth
• wbt – wireless and Bluetooth
• nw – networking and wireless

Here's a video breakdown of the lettering:

In many cases, the base model is upgradeable to add these features one by one. If a small company is just starting out, the base model may be sufficient in the beginning, but as business increases, additional features may be required. Alternatively, if an established company is in need of a fully-loaded machine, the various model types with included features are available upfront.