another thing; exception; special case
プロの技術は素人とは別物だ。
The skill of a professional is something entirely different from an amateur's.
手作りと市販品は別物だと感じる。
I feel that handmade and store-bought items are different things.
見た目は似ているが中身はまったく別物である。
They look similar, but the contents are completely different.