The Idiom Attic - a collection of hundreds of English idioms, each one explained.
The meaning of "lame duck"
" Lame duck "
A person or thing that is no longer properly able to function. Also, more specifically, a person in authority, for example a president or prime minister, in their final period of office after a successor has already been elected.
The boss is pretty much a lame duck now that he's announced his retirement and we know he won't be here next month.