Definition of "pigswill"

He came down the slope towards the church at speed, holding his breath against the smell of warmed pigswill from the sty.

2022, Ian McEwan, Lessons, page 179

‘With respect, Professor...’‘Pigswill! You don't respect me. You fear me, are irritated by me, envy me... you everything me, but you do not respect me.’

1991, Stephen Fry, The Liar, London: Heinemann, page 50