According to LawNewz, the Trump administration is now regularly using a term that has rarely been used by the federal government since 2009:

There has been a shift in the language that the U.S. Department of Justice is using in its press releases and official announcements, and it’s not sitting well with some. The DOJ, under the leadership of Attorney General Jeff Sessions, has begun using the term “illegal aliens” to refer to immigrants who do not have the proper paperwork to be in the United States.

Under Obama, the de rigueur term was “undocumented” which sanitized what was going on. As the Chicago Tribune complains:

[I]n the July 9, 2014, announcement, “Department of Justice Announces New Priorities to Address Surge of Migrants Crossing into the U.S.,” then-Deputy Attorney General James Cole chose such language as “migrants,” “asylum seekers” and “unaccompanied minors.”

Naturally, a lot of people who aren’t fans of Sessions are displeased:

“They’re using a legally inaccurate term that’s deployed to unfairly label and scapegoat people who are out of status due to a variety of systemic circumstances,” Xakota Espinoza from the Center for Racial Justice Innovation, told LawNewz.com
…
“The i-word is legally inaccurate, politically loaded, dehumanizing to the people it describes and likely unintentionally fuels racial profiling and violence directed toward immigrants,” Espinoza explained.

Department of Justice referring to people here as what they are, illegal aliens, brings a level of clarity to the issue that had been obscured in a cloud of legalese and motivations.