From the introduction to Lame Duck Sessions of Congress Following a Majority-Changing Election: In Brief (R45402, Nov. 13, 2018):
“Lame duck” sessions of Congress take place whenever one Congress meets after its successor is elected but before the term of the current Congress ends. Their primary purpose is to complete action on legislation. They have also been used to prevent recess appointments and pocket vetoes, to consider motions of censure or impeachment, to keep Congress assembled on a standby basis, or to approve nominations (Senate only). In recent years, most lame duck sessions have focused on program authorizations, trade-related measures, appropriations, and the budget.