Um may refer to:

• Um, an exclamation or filled pause in spoken conversation
• United Motors Company
• Um (Korean name)
• .um, the Top Level Domain for United States Minor Outlying Islands
• µm for micrometre, sometimes used with a limited character set
• Um interface, the air interface for the GSM mobile telephone standard
• Unofficial magistrate, as a postnominal

.um was the Internet country code top-level domain for the United States Minor Outlying Islands. It was administered by the United States Minor Outlying Islands Registry. Until late 2006 USMIR was housed at the University of Southern California Information Sciences Institute (USC-ISI), which was the original administrator of .us prior to NeuStar absorbing that role.